Inform PendingIntent sender if broadcast was not queued.

If the broadcast could not be queued due to a stopped user, the
party trying to send a PendingIntent should be notified right away.
Otherwise, for instance, AlarmManager could be waiting forever to
be called back after the broadcast is delivered.

This is a potential fix for:
Bug: 18290018

Change-Id: I07c0751e80f11e69dfa2be5c96a033aecb298b81