Fix NPE when user goes into maps navigation mode and tries to split app.

OnDestroy is called in this scenario and mContainer is set to null. When I added this code I assumed this will be non null always.

Test: Manual : open maps->start navigation-> overview->split
Fix: 376409147
Flag: EXEMPT bugfix
Change-Id: I96a47b24beb5b3d343aae0e715c0b3efabdebe08