autorevert ends up calling vc-git-find-file-hook multiple times. When
this happens, smerge restarts and goes to the next hunk. This is not
desired when in the middle of an edit. To fix, don’t start smerge when
smerge is already enabled.
Related to https://lists.gnu.org/archive/html/emacs-devel/2015-10/msg02201.html
Attached is a patch that avoids this bug.
-Matthew