Avoid IllegalStateException while editing label

Bug: 32333918
Bug: 32332232

It appears the IME can deliver events after the fragment has saved
its state. Defensive code now stops listening for IME events when the
fragment view is destroyed. It also calls dismissAllowingStateLoss() to
be more resilient to this problem.

Change-Id: I3139c7f56596e148e9179035562f80e9fc232cf4