Add null check for cutouts on display change

DisplayLayout#getDisplayCutout() is @Nullable
so we should have a null check before potentially
preventing stashing upon display change based
on the cutout information.

The original cutout check was introduced by ag/35066396

Bug: 441665422
Flag: EXEMPT bugfix
Test: rotate PiP on a display w/o cutouts
Change-Id: I1a0b6e87bc27252b9dc5f1eb4f0320a467973d1a