Make sure we hold on to pending undo ops.

its possible the converesation list fragment isn't visible yet, since
onepanecontroller doens't always have it around.

In this case, store the pending action in the activity and show it
once the fragments attaches.

Fixes b/6779210 Deleting a Conversation in a Label in Conversation View Does Not Show Undo

Change-Id: Ib8c41dceef67dcdac1c331ed777daf6dfb0b6702
5 files changed