Implemented GL_SAMPLER_BINDING query

Sampler objects already exist, only the query was missing.

Change-Id: Iea4a65ee4af149a33b262eba4fc0d6256775d1e1
Reviewed-on: https://swiftshader-review.googlesource.com/4746
Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>
diff --git a/src/OpenGL/libGLESv2/Context.cpp b/src/OpenGL/libGLESv2/Context.cpp
index 8040da8..05dd548 100644
--- a/src/OpenGL/libGLESv2/Context.cpp
+++ b/src/OpenGL/libGLESv2/Context.cpp
@@ -2338,8 +2338,7 @@
 		*params = GL_BACK;

 		break;

 	case GL_SAMPLER_BINDING: // GLint, default 0

-		UNIMPLEMENTED();

-		*params = 0;

+		*params = mState.sampler[mState.activeSampler].name();

 		break;

 	case GL_UNIFORM_BUFFER_BINDING: // name, initially 0

 		if(clientVersion >= 3)