Don't check for vertex buffers in dispatch aspects

Recently started causing a crash because we stopped creating an empty
InputState for compute pipelines

src/tests/unittests/validation/ComputeValidationTests.cpp

@@ -0,0 +1,20 @@
+// Copyright 2017 The NXT Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "ValidationTest.h"
+
+class ComputeValidationTest : public ValidationTest {
+};
+
+//TODO(cwallez@chromium.org): Add a regression test for Disptach validation trying to acces the input state.