avoid crash in unit test due to global objects

The lifecycle of the XFrame and the XController are both correct but
getCurrentController has already been reset when the
SidebarController::dispose is called.

This avoids then calling the XController destructor during exit when
taking a SolarMutex is a problem.

Change-Id: I54470f091e506fb397e2424d2d3c4ac051cae924

sfx2/source/sidebar/SidebarController.cxx

@@ -221,16 +221,11 @@ void SAL_CALL SidebarController::disposing()
             aDeck.disposeAndClear();
     }
 
-    SidebarControllerContainer::iterator iEntry (maSidebarControllerContainer.find(mxFrame->getController()));
-    if (iEntry != maSidebarControllerContainer.end())
-        maSidebarControllerContainer.erase(iEntry);
+    uno::Reference<css::frame::XController> xController = mxFrame->getController();
+    if (!xController.is())
+        xController = mxCurrentController;
 
-    css::uno::Reference<css::ui::XContextChangeEventMultiplexer> xMultiplexer (
-        css::ui::ContextChangeEventMultiplexer::get(
-            ::comphelper::getProcessComponentContext()));
-    if (xMultiplexer.is())
-        xMultiplexer->removeAllContextChangeEventListeners(
-            static_cast<css::ui::XContextChangeEventListener*>(this));
+    unregisterSidebarForFrame(this, xController);
 
     if (mxReadOnlyModeDispatch.is())
         mxReadOnlyModeDispatch->removeStatusListener(this, Tools::GetURL(gsReadOnlyCommandName));