Fix unecessary and ill-timed MR emails
Overview
There are a few issues being observed with MR emails.
Issue 1 - No commit email
I am fine with that, because I chose to create an empty MR (and it's WIP anyway).
Should we restrict this email to conflicts-only @lulalala?
Issue 2 - "Source branch is missing" email after merge
(See https://gitlab.com/gitlab-org/gitlab-ce/issues/48409)
Sometimes after merging an MR, an email is sent saying the MR cannot be merged.
Edited by Paul Slaughter