Avoid member call through null this pointer

...as seen with UBSan during newly introduced UITest_goalSeek (where eOldActive
is 0 and all four members of pGridWin except for pGridWin[2] are null):

> sc/source/ui/view/tabview3.cxx:1814:45: runtime error: member call on null pointer of type 'vcl::Window'
>  #0 in ScTabView::SetTabNo(short, bool, bool, bool) at sc/source/ui/view/tabview3.cxx:1814:45 (instdir/program/../program/libsclo.so +0xb25dfca)
>  #1 in ScTabViewShell::DoReadUserDataSequence(com::sun::star::uno::Sequence<com::sun::star::beans::PropertyValue> const&) at sc/source/ui/view/tabvwsh4.cxx:500:5 (instdir/program/../program/libsclo.so +0xb2d27a5)
>  #2 in ScTabViewShell::ReadUserDataSequence(com::sun::star::uno::Sequence<com::sun::star::beans::PropertyValue> const&) at sc/source/ui/view/tabvwsh4.cxx:491:9 (instdir/program/../program/libsclo.so +0xb2d245a)
>  #3 in SfxBaseController::ConnectSfxFrame_Impl(SfxBaseController::ConnectSfxFrame) at sfx2/source/view/sfxbasecontroller.cxx:1368:52 (instdir/program/libsfxlo.so +0x320c974)
>  #4 in SfxBaseController::attachFrame(com::sun::star::uno::Reference<com::sun::star::frame::XFrame> const&) at sfx2/source/view/sfxbasecontroller.cxx:550:13 (instdir/program/libsfxlo.so +0x32055f1)
>  #5 in (anonymous namespace)::SfxFrameLoader_Impl::impl_createDocumentView(com::sun::star::uno::Reference<com::sun::star::frame::XModel2> const&, com::sun::star::uno::Reference<com::sun::star::frame::XFrame> const&, comphelper::NamedValueCollection const&, rtl::OUString const&) at sfx2/source/view/frmload.cxx:593:18 (instdir/program/libsfxlo.so +0x319fcdd)
>  #6 in (anonymous namespace)::SfxFrameLoader_Impl::load(com::sun::star::uno::Sequence<com::sun::star::beans::PropertyValue> const&, com::sun::star::uno::Reference<com::sun::star::frame::XFrame> const&) at sfx2/source/view/frmload.cxx:710:13 (instdir/program/libsfxlo.so +0x319b263)
>  #7 in framework::LoadEnv::impl_loadContent() at framework/source/loadenv/loadenv.cxx:1148:37 (instdir/program/../program/libfwklo.so +0xfa4cc8)
>  #8 in framework::LoadEnv::startLoading() at framework/source/loadenv/loadenv.cxx:382:20 (instdir/program/../program/libfwklo.so +0xf9a76a)
>  #9 in framework::LoadEnv::loadComponentFromURL(com::sun::star::uno::Reference<com::sun::star::frame::XComponentLoader> const&, com::sun::star::uno::Reference<com::sun::star::uno::XComponentContext> const&, rtl::OUString const&, rtl::OUString const&, int, com::sun::star::uno::Sequence<com::sun::star::beans::PropertyValue> const&) at framework/source/loadenv/loadenv.cxx:168:14 (instdir/program/../program/libfwklo.so +0xf97d15)
>  #10 in framework::Desktop::loadComponentFromURL(rtl::OUString const&, rtl::OUString const&, int, com::sun::star::uno::Sequence<com::sun::star::beans::PropertyValue> const&) at framework/source/services/desktop.cxx:618:12 (instdir/program/../program/libfwklo.so +0x108e918)
>  #11 in non-virtual thunk to framework::Desktop::loadComponentFromURL(rtl::OUString const&, rtl::OUString const&, int, com::sun::star::uno::Sequence<com::sun::star::beans::PropertyValue> const&) at framework/source/services/desktop.cxx (instdir/program/../program/libfwklo.so +0x108e9ca)
>  #12 in gcc3::callVirtualMethod(void*, unsigned int, void*, _typelib_TypeDescriptionReference*, bool, unsigned long*, unsigned int, unsigned long*, double*) at bridges/source/cpp_uno/gcc3_linux_x86-64/callvirtualmethod.cxx:77:5 (instdir/program/libgcc3_uno.so +0xba96d)
>  #13 in cpp_call(bridges::cpp_uno::shared::UnoInterfaceProxy*, bridges::cpp_uno::shared::VtableSlot, _typelib_TypeDescriptionReference*, int, _typelib_MethodParameter*, void*, void**, _uno_Any**) at bridges/source/cpp_uno/gcc3_linux_x86-64/uno2cpp.cxx:233:13 (instdir/program/libgcc3_uno.so +0xb6855)
>  #14 in unoInterfaceProxyDispatch at bridges/source/cpp_uno/gcc3_linux_x86-64/uno2cpp.cxx:420:13 (instdir/program/libgcc3_uno.so +0xb4663)
>  #15 in binaryurp::IncomingRequest::execute_throw(binaryurp::BinaryAny*, std::__debug::vector<binaryurp::BinaryAny, std::allocator<binaryurp::BinaryAny> >*) const at binaryurp/source/incomingrequest.cxx:236:13 (instdir/program/libbinaryurplo.so +0x209ede)
>  #16 in binaryurp::IncomingRequest::execute() const at binaryurp/source/incomingrequest.cxx:79:26 (instdir/program/libbinaryurplo.so +0x205f10)
>  #17 in request at binaryurp/source/reader.cxx:85:9 (instdir/program/libbinaryurplo.so +0x2966d3)
>  #18 in cppu_threadpool::JobQueue::enter(long, bool) at cppu/source/threadpool/jobqueue.cxx:107:17 (instdir/program/libuno_cppu.so.3 +0x17e863)
>  #19 in cppu_threadpool::ORequestThread::run() at cppu/source/threadpool/thread.cxx:165:31 (instdir/program/libuno_cppu.so.3 +0x1977bb)
>  #20 in threadFunc at include/osl/thread.hxx:185:15 (instdir/program/libuno_cppu.so.3 +0x1a0347)
>  #21 in osl_thread_start_Impl(void*) at sal/osl/unx/thread.cxx:234:9 (instdir/program/libuno_sal.so.3 +0x2e6789)
>  #22 in start_thread at /usr/src/debug/glibc-2.27-56-g50df56ca86/nptl/pthread_create.c:463:7 (/lib64/libpthread.so.0 +0x7593)
>  #23 in __GI___clone at /usr/src/debug/glibc-2.27-56-g50df56ca86/misc/../sysdeps/unix/sysv/linux/x86_64/clone.S:95 (/lib64/libc.so.6 +0xfa00e)

Change-Id: I23fb29cdec429a1bbdba3c04f3c3c66ad744621e
Reviewed-on: https://gerrit.libreoffice.org/56224Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
Tested-by: Stephan Bergmann <sbergman@redhat.com>

sc/source/ui/view/tabview3.cxx

@@ -1810,7 +1810,7 @@ void ScTabView::SetTabNo( SCTAB nTab, bool bNew, bool bExtendSelection, bool bSa
         }
 
         ScSplitPos eOldActive = aViewData.GetActivePart();      // before switching
-        bool bFocus = pGridWin[eOldActive]->HasFocus();
+        bool bFocus = pGridWin[eOldActive] && pGridWin[eOldActive]->HasFocus();
 
         aViewData.SetTabNo( nTab );
         // UpdateShow before SetCursor, so that UpdateAutoFillMark finds the correct