[Search git status] cover all possible unmerged statuses

In PatrickF1#262, my research showed
that only 4 of the 7 unmerged statuses listed in git status' help were
possible. However, upon experimentation, I realized all 7 are possible.
The three I left out are easily reproducible by merging two branches
that renamed the same file but to different names. In this commit, I
add them back in.

functions/_fzf_preview_changed_file.fish

@@ -9,7 +9,7 @@ function _fzf_preview_changed_file --argument-names path_status --description "S
     # https://fishshell.com/docs/current/fish_for_bash_users.html
     set -l path (string unescape (string sub --start 4 $path_status))
     # first letter of short format shows index, second letter shows working tree
-    # https://git-scm.com/docs/git-status/2.35.0#_output
+    # https://git-scm.com/docs/git-status/2.35.0#_short_format
     set -l index_status (string sub --length 1 $path_status)
     set -l working_tree_status (string sub --start 2 --length 1 $path_status)
     # no-prefix because the file is always being compared to itself so is unecessary
@@ -18,9 +18,10 @@ function _fzf_preview_changed_file --argument-names path_status --description "S
     if test $index_status = '?'
         _fzf_report_diff_type Untracked
         _fzf_preview_file $path
-    else if contains {$index_status}$working_tree_status UD DU UU AA
-        # inferred from # https://stackoverflow.com/questions/22792906/how-do-i-produce-every-possible-git-status
-        # the above 4 statuses are the only possible ones for a merge conflict
+    else if contains {$index_status}$working_tree_status DD AU UD UA DU AA UU
+        # Unmerged statuses taken directly from git status help's short format table
+        # Unmerged statuses are mutually exclusive with other statuses, so if we see
+        # these, then safe to assume the path is unmerged
         _fzf_report_diff_type Unmerged
         git diff $diff_opts -- $path
     else