Fix attachment loading in Exchange.

1) For pre 2010 versions, attachment loading was 100% busted
   due to a null pointer.
2) Attachment status callbacks are now in theory happening
   correctly.

Bug: 9735207
Bug: 9842867
Change-Id: Iddaab725b7411eecbfc7c35e9a4bc7214630b83c
5 files changed