Decoding MMS attachments does not work under certain circumstances

As reported by Craftyguy:

When using Chatty/mmsd, the attachment will include some of the SMIL as well as the attachment. This is likely traced back to the fact that the decoding of the MMS on mmsd points to the wrong start point of the attachment, as chatty does not attempt to decode the attachments, it just uses the start points given it to by mmsd.

kop316 cannot reproduce this issue, but is putting it on here in case this is seen by anyone else.