Merge pull request #9914 from asutherland/email-zero-length-bodies

Bug 874405 - [email/IMAP] snippet/partial body fetch breaks on zero-length bodies. r=jrburke(cherry picked from commit aa8364e96ac8a0eef019a73be5efef6df882c86f)
Merge pull request #9956 from alivedise/bugzilla/875262

Bug 875262 - Default channel on lockscreen is notification r=davidflanagan(cherry picked from commit 5bfd97ef33c3526c9f26a15ab8f51d933d03baf6)