Suppressing Illegal argument exception when activating a task.

It's always possible to have race conditions when the button is still present
in Shelf Recents, but the task has gone, and we don't want sustemui to crash
when this happens.

Bug: 20024603
Change-Id: I96a3ebbc3217bcd74994d4a626d07824c7bb82e5
1 file changed