Prevent dialog launch from crashing in rare cases

This CL ensures that we don't call GhostView.addGhost on a source
that triggered a dialog launch if that source was just removed from its
hierarchy.

The end result of this CL is not perfect given that it makes the dialog
animate from the Rect at (0, 0, 0, 0) but it should be rare enough to
not matter.

Bug: 295858408
Test: Manual. Patched the code to first confirm that this was the source
of the bug then confirmed that the fix worked.

Change-Id: I51ed0f698649d135334d699925b75976352be55a