'main': Fix highlighting of null execs.

Fixes #676.

highlighters/main/main-highlighter.zsh

@@ -824,6 +824,10 @@ _zsh_highlight_main_highlighter_highlight_list()
       next_word=${next_word//:regular:/}
       next_word+=':sudo_opt:'
       next_word+=':start:'
+      if [[ $arg == 'exec' ]]; then
+        # To allow "exec 2>&1;" where there's no command word
+        next_word+=':regular:'
+      fi
      else
       case $res in
         reserved)       # reserved word

highlighters/main/test-data/null-exec.zsh

@@ -34,5 +34,5 @@ expected_region_highlight=(
   '1 4 precommand' # exec
   '6 6 redirection' # >
   '7 15 path' # /dev/null
-  '16 16 commandseparator "issue #676"' # ;
+  '16 16 commandseparator' # ;
 )