Fix crash when removing a display with activities

When secondary display is removed current behavior is to
move its stacks to the primary display. This requires app
windows to be reparented, and there was a check missing
for app windows in DisplayContent.reParentWindowToken.

Test: bit FrameworksServicesTests:com.android.server.wm.DisplayContentTests
Test: #testMoveStackBetweenDisplays
Bug: 33677605
Change-Id: I2ac2cdba273134438c63385887a09c37d42017bb
2 files changed