Bug 1090043 - [B2G][Message] MMS attachments missed in SMIL could not be displayed

- Check if the attachment count match the SMIL and force to parse without SMIL if the count is unmatched
- Make sure mimetype 'application/***' is visible in thread (parseWithoutSMIL case) 
while you're here, how about changing this to `slides = Array(attachments.length)` so that we don't have a sparse array? (found this a few days ago but didn't change it :) )