HLSL: Fix #1215: propagate error on seeing a type name instead of a variable.

hlsl/hlslGrammar.cpp

@@ -3051,6 +3051,8 @@ bool HlslGrammar::acceptPostfixExpression(TIntermTyped*& node)
         }
         if (! peekTokenClass(EHTokLeftParen)) {
             node = parseContext.handleVariable(idToken.loc, fullName);
+            if (node == nullptr)
+                return false;
         } else if (acceptFunctionCall(idToken.loc, *fullName, node, nullptr)) {
             // function_call (nothing else to do yet)
         } else {