[FIX] sap.uxap.ObjectPageLayout: Fixed error on section destroy
[FIX] sap.uxap.ObjectPageLayout: Fixed error on section destroy

When in ObjectPageLayout we use IconTabBar and destroy an
sap.uxap.ObjectPageSection and then rerender the layout
the setter for the selectedSectionId is updated after the DOM is rendered
and its value is read in "onBeforeRendering" it doesn`t return a dom reference
to the deleted section and "TypeError" has been thrown.

Change-Id: Iec03fb437cab618e1e1119a5ba707e2ee99632c0
BCP: 1980214073

SAP/openui5,SAP/openui5,SAP/openui5,SAP/openui5