Fix crash when handling touch on caption

http://ag/20355140 moved drag detection outside the switch block.
It now can be true when we are not going to handle the touch.
Add extra check for mShouldHandleEvents before processing ACTION_UP or
ACTION_CANCEL.

Bug: 259297955
Test: touch down outside the window, in caption area, drag finger and
  release
Test: attach a bluetooth mouse and resize the window from sides
Change-Id: I6645479eb1709e68ade87d2d7e7babdf99f232aa