Don't crash when we get a drag-ended after being detached
Don't crash when we get a drag-ended after being detached

Removing view groups during a drag would cause an NPE here.  The
child views will still get the drag-ended event as expected.

Bug 8298439

Change-Id: I665ba1d139e8aaa820f5f515186bc4ce8bcdb1ea

xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base