SF: check secure layers in screenshot message handler

- Instead of checking for the presence of secure layers on the Binder
  thread, check in the message handler. Transactions may have occurred
  in between when the check is done and when the screen shot message
  is handled.

Bug 23757877

Change-Id: Iec74193996ca72c60f86f7c0f0b2a5dea8d19543