'main': Fix an issue whereby a --option was highlighted as a file

Regression test included.

Fixes #578.

Review-by: Matthew Martin

highlighters/main/main-highlighter.zsh

@@ -1045,9 +1045,10 @@ _zsh_highlight_main_highlighter_highlight_argument()
         highlights+=($reply)
         ;;
       '$')
-        path_eligible=0
+        if [[ $arg[i+1] != "'" ]]; then
+          path_eligible=0
+        fi
         if [[ $arg[i+1] == "'" ]]; then
-          path_eligible=1
           _zsh_highlight_main_highlighter_highlight_dollar_quote $i
           (( i = REPLY ))
           highlights+=($reply)