Add leash check in PipTaskOrganizer#fadeExistingPip

Bug: 197319184
Test: N/A, not sable to reproduce the issue, adding protection based on
      the stack trace
Change-Id: I6363dd425eac6332f59fe1fed074c6518227580f
(cherry picked from commit 4353053c)
Merged-In:I6363dd425eac6332f59fe1fed074c6518227580f