IME : Fix sym key regression

http://review.cyanogenmod.org/#/c/25787/2 caused the "dismiss" arrow
for ime's to execute back action as well. Reproducible via :

Open sms app->Open message thread->Tap message field->Tap downward arrow on navbar

Expected behaviour : Keyboard should be dismissed
Actual behaviour : Keyboard is dismissed and user is taken to previous screen.

Change-Id: I6ab65b00464fb6e00849d7fd6c8bd438b23ee76b