Resume next activity if pausing app died

If the top activity is crashed before showing any window, when its
process reported dead, it will be regarded as no visible activity
and no need to resume next activity. That may lead to the next top
activity remains in paused state and may be unresponsive.

Bug: 159951007
Test: atest ActivityTaskManagerServiceTests# \
      testResumeNextActivityOnCrashedAppDied
Change-Id: I635fceb9cf7b782f6ffbb9ebef7cb69053f64a0b