Fixed bug in light transport uv->position 'unwrap'.

Assets/ScriptableRenderPipeline/HDRenderPipeline/ShaderPass/ShaderPassLightTransport.hlsl

 
     // Output UV coordinate in vertex shader
     if (unity_MetaVertexControl.x)
-    {
-        // OpenGL right now needs to actually use incoming vertex position,
-        // so use it in a very dummy way
-        //v.positionOS.z = vertex.z > 0 ? 1.0e-4 : 0.0;
-    }
+
-    {
-        // OpenGL right now needs to actually use incoming vertex position,
-        // so use it in a very dummy way
-        //v.positionOS.z = vertex.z > 0 ? 1.0e-4 : 0.0;
-    }
+
+    // Zero out the Z component. However, OpenGL right now needs to actually use the incoming vertex
+    // position, so also take this opportunity to create a dependence on it.
+    inputMesh.positionOS.z = inputMesh.positionOS.z > 0 ? 1.0e-4 : 0.0;
 
     float3 positionWS = TransformObjectToWorld(inputMesh.positionOS);
     output.vmesh.positionCS = TransformWorldToHClip(positionWS);