[css mode] Fix tokenizing of empty url() token

Issue #2465

Author: marijnh

mode/css/css.js

@@ -84,7 +84,7 @@ CodeMirror.defineMode("css", function(config, parserConfig) {
 
   function tokenParenthesized(stream, state) {
     stream.next(); // Must be '('
-    if (!stream.match(/\s*[\"\']/, false))
+    if (!stream.match(/\s*[\"\')]/, false))
       state.tokenize = tokenString(")");
     else
       state.tokenize = null;

mode/css/test.js

@@ -116,4 +116,7 @@
      "  [property src]: [atom url]([string http://blah]),",
      "    [atom url]([string http://foo]);",
      "}");
+
+  MT("empty_url",
+     "[def @import] [tag url]() [tag screen];");
 })();