Only clear mInputMethodInputTarget if it is moved to the new display

onDisplayChanged can also be invoked when the configuration is
changed on the display. In this case, we should not clear
mInputMethodInputTarget.

Bug: 154108034
Test: atest MultiDisplayClientTests
Change-Id: Ic6d9bcb12fde5f7718f9475f228bab33aac49d25
1 file changed