Fix possible crash during delivery delay

This is reproducible in conversations with many messages
(e.g. 7800 messages on SGS3).

Change-Id: I26a7b989c9d27da34481f20f358a9e09bb4a2ef6
Merge branch 'cm-11.0' of github.com:CyanogenMod/android_packages_apps_Mms into cm-11.0