Return pending intent to service caller if MmsService can't be connected

If MmsService can not be connected, broker throws a runtime exception
which does not return to service caller via PendingIntent. MMS app would
wait forever for the return of sent/downloaded PendingIntent. This
change makes sure PendingIntent is always returned so MMS app can be
unblocked.

b/19732709

Change-Id: I694a0fc29bb431b48c7077e7a323844709ae695f