Bug 1003843 - Follow up to Bug 951676 - [Messages][Refresh] Add specific image in case of more than one recipient in the list threads. r=schung

I'm not sure this is correct though; maybe we should look at the dataset (I think we have a isDraft property there).

I don't exactly remember, but I think drafts' "threadId" start with "draft-" so in that case it's good enough. But I'm not sure and the code around drafts is not _so_ simple :/