HLSL: Address #839: avoid crash by distinguishing between bad argument and no argument.

hlsl/hlslGrammar.cpp

@@ -2926,11 +2926,16 @@ bool HlslGrammar::acceptArguments(TFunction* function, TIntermTyped*& arguments)
     if (! acceptTokenClass(EHTokLeftParen))
         return false;
 
+    // RIGHT_PAREN
+    if (acceptTokenClass(EHTokRightParen))
+        return true;
+
+    // must now be at least one expression...
     do {
         // expression
         TIntermTyped* arg;
         if (! acceptAssignmentExpression(arg))
-            break;
+            return false;
 
         // hook it up
         parseContext.handleFunctionArgument(function, arguments, arg);