Bug 1070429 - [email/IMAP] premature saving leads to missing bodies. r=jrburke

propagate back-end fix
https://github.com/mozilla-b2g/gaia-email-libs-and-more/pull/343
Merge pull request #24927 from asutherland/email-getbody-fix

Bug 1070429 - [email/IMAP] premature saving leads to missing bodies. r=jrburke

propagation of mozilla-b2g/gaia-email-libs-and-more#343