BackgroundFallback: Cover all cases where the fallback is needed

Fixes an issue where uncovered regions were not
covered if they are to the right or bottom of the
content view.

Fixes: 78661186
Test: Install test app from bug, enable cuotut, open test app, go to landscape, verify white fallback background is drawn in both landscape and seascape
Test: atest BackgroundFallbackTest
Change-Id: I442f03395a71550a534d64233762aa84002319dd