use dummy semicolon to create mixin call with one argument containing

comma separated css list. fix #33

src/com/inet/lib/less/LessParser.java

@@ -1106,16 +1106,15 @@ private Expression concat( Expression left, char operator, Expression right ) {
         if( left == null ) {
             return right;
         }
-        if( right == null ) {
-            return left;
-        }
         Operation op;
         if( left.getClass() == Operation.class && ((Operation)left).getOperator() == operator ) {
             op = (Operation)left;
         } else {
             op = new Operation( reader, left, operator );
         }
-        op.addOperand( right );
+        if( right != null ) {
+            op.addOperand( right );
+        }
         return op;
     }
 

test/com/inet/lib/less/samples/less_org_doc/mixins/MultipleParameters.css

@@ -3,3 +3,8 @@
   color-2: #008000;
   padding-2: 2;
 }
+.dummyParameter {
+  color-1: 1, 2, 3;
+  color-2: 1, 2, 3;
+  padding-2: 2;
+}

test/com/inet/lib/less/samples/less_org_doc/mixins/MultipleParameters.less

@@ -15,4 +15,7 @@
 }
 .some .selector div {
   .mixin(#008000);
-}
+}
+.dummyParameter {
+  .mixin(1, 2, 3;)
+}