[INTERNAL] sap.uxap.ObjectPageLayout - do not trigger calculations when size is 0
[INTERNAL] sap.uxap.ObjectPageLayout - do not trigger calculations when size is 0

BCP: 1780338528
The _onUpdateScreenSize method triggers heavy calculations and also resets the
scroll position to 0, which in turn toggles the header.
This change prevents all this when the object page is resized to zero (f.e. by navigation)
indirectly fixing the problem, reported in issue 1780338528.

Change-Id: I3aacc6f11c82c7571165d1d07ede3f9bcacd59ec

SAP/openui5,cschuff/openui5,SAP/openui5,cschuff/openui5,SQCLabs/openui5,SQCLabs/openui5,cschuff/openui5,nzamani/openui5,SAP/openui5,nzamani/openui5,nzamani/openui5,SAP/openui5,SQCLabs/openui5