Reattach LauncherAppWidgetHostView to its parent after canceling drag

onDrop isn't called if the drag is canceled at Launcher.onPause. Let's
also reattach LauncherAppWidgetHostView to its parent in this case.

Test: long press and hold a widget and, at the same time, press the
      power button. Don't let go of the long press and press the power
      button. No crash observed.
Fix: 190950646
Change-Id: Id52a51291863b7ef63c861eb6dc23b015484be65