Backport #34512 by tclin914
If the message from form.MergeMessageField is empty, we will miss a "\n"
between the title and the "Co-authored-by:" line. The title and message
should have a blank line between of them.
Co-authored-by: Jim Lin <jim@andestech.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>