add test shader for issue #213

Author: floooh

test/issue213_unused_ub.glsl

@@ -0,0 +1,12 @@
+@vs vs
+layout(binding=0) uniform vs_params {
+    float unused;
+};
+void main() {}
+@end
+
+@fs fs
+void main() {}
+@end
+
+@program shader vs fs