Fix CrossAppDragAndDropTests failed

Currently, InputDispatcher could report the invalid drop target when
receving an unexpected cancel or the drag window has gone. In other
hand,`View.cancelDragAndDrop` could directly cancel the current drag
state cause `reportDropWindow` access the invalid state.

We should check the valid drag state when called `reportDropWindow`.

Test: atest DragDropControllerTests CrossAppDragAndDropTests
Bug: 234889646
Change-Id: Ibe9c94d2ff4471bfc5ff32d62e4701ef9a0d75d0