uitest: fix small bug when trying to select different sheet in calc

Change-Id: I83e2b8dc1b0da9f28475994493e3776c898a5729
Reviewed-on: https://gerrit.libreoffice.org/50853Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>

sc/source/ui/uitest/uiobject.cxx

@@ -131,7 +131,9 @@ void ScGridWinUIObject::execute(const OUString& rAction,
             auto itr = rParameters.find("TABLE");
             const OUString rStr = itr->second;
             sal_Int32 nTab = rStr.toUInt32();
-            mxGridWindow->getViewData()->SetTabNo(nTab);
+            ScTabView* pTabView = mxGridWindow->getViewData()->GetView();
+            if (pTabView)
+                pTabView->SetTabNo(nTab);
         }
         else if (rParameters.find("OBJECT") != rParameters.end())
         {