DO NOT MERGE Fix the cutout of magnification border

If the window is unmagnifiable, it might cause the cutout of
magnification region.
To fix it, we set the flag when the touchable region is not the
entier window frame.

Bug: 196510717
Test: manual test on gestural and 3-button navigation
Change-Id: Ida2bb5bf120038ac9153e12790b93bdec195adbc