MMS: MMS Status won't update if chatty is closed and reopened

In chatty_mm_account_recieve_mms_cb (), chatty can only update the status of an MMS if chatty_mm_chat_find_message_with_id () finds the message. However, this will fail if chatty is closed and reopened (because all of the ids are cleared).

It would be nice to have a chatty_mm_chat_find_message_with_uid () function to check if chatty_mm_chat_find_message_with_id () fails, so that chatty_mm_account_recieve_mms_cb () can find the correct message to update.