Improve handling of TV PiPs bigger than movement bounds

For very tall/wide expanded PiPs, the positioning algorithm considered
the anchor position as invalid, as it crossed the movement bounds.
It assumed that if no free valid position is found the PiP must be
stashed and there exist keep clear areas overlapping the unstash
position that caused that stashing. But in the case of these big PiPs
there were no overlapping keep clear areas, resulting in a NPE.

This change improves handling of oversize PiPs, allowing the anchor
position to cross movement bounds without stashing, and improves null
safety when searching for the stash position.

Bug: 228948019
Test: atest TvPipKeepClearAlgorithmTest
Change-Id: I6a7c6c316d03ca8902b9cfb1e0c4abcb873eff18