Don't try to show crash dialog if lock screen is showing.

The crash dialog doesn't show on top of the lock screen so
don't try to display the crash dialog in this case so that
the process can be killed right way instead of waiting for
the user to interact with the crash dialog that isn't visible.

Bug: 31395870
Change-Id: Ic1ce9a133ea12cee8a27690004ac3b56cf75808b