Fix '@arguments' behaviour, Closes #632

`.mixin` & `.mixin()` had differing behaviours.

lib/less/parser.js

@@ -763,7 +763,7 @@ less.Parser = function Parser(env) {
                     }
 
                     if (elements.length > 0 && ($(';') || peek('}'))) {
-                        return new(tree.mixin.Call)(elements, args, index, env.filename, important);
+                        return new(tree.mixin.Call)(elements, args || [], index, env.filename, important);
                     }
                 },
 

test/css/mixins-args.css

@@ -59,6 +59,9 @@ body {
 .arguments2 {
   border: 0px;
 }
+.arguments3 {
+  border: 0px;
+}
 .edge-case {
   border: "{";
 }

test/less/mixins-args.less

@@ -116,6 +116,9 @@ body {
 .arguments2 {
     .mixin-arguments();
 }
+.arguments3 {
+    .mixin-arguments;
+}
 
 // Edge cases