Finish blocking activity when it goes invisible.

This way we avoid potential stale string when the blocking activity is
re-surfaced.

Change-Id: Ife17ef765822797be87f49942e143656319d5b47
Fixes: 113126734
Test: tested on device
(cherry picked from commit fdfeeb087c4a5d50f2b33eb6a6f09c4b6ac933cb)
1 file changed