Bug 824783 - [email] "No mail in this Folder" overlaps the actual emails in the sent folder if the phone times out. regression fix, a=bustage-fix

A review comment was addressed, but the code put in the wrong place.
This regressed IMAP's ability to sync into the past.  This was
reflected in some of the IMAP unit tests failing.  With this correction,
the IMAP tests are all green again.

fix breakage from https://github.com/mozilla-b2g/gaia-email-libs-and-more/pull/104