[metal] skip screen-space AABBs compute job if no lights, fixes api validation error in the editor on some situations

Assets/ScriptableRenderLoop/HDRenderPipeline/Lighting/TilePass/TilePass.cs

                 var cmd = new CommandBuffer() { name = "" };
 
                 // generate screen-space AABBs (used for both fptl and clustered).
+                if (m_lightCount != 0)
                 {
                     temp.SetRow(0, new Vector4(1.0f, 0.0f, 0.0f, 0.0f));
                     temp.SetRow(1, new Vector4(0.0f, 1.0f, 0.0f, 0.0f));

Assets/ScriptableRenderLoop/fptl/FptlLighting.cs

             var cmd = new CommandBuffer() { name = "Build light list" };
 
             // generate screen-space AABBs (used for both fptl and clustered).
+            if (numLights != 0)
             {
                 var proj = CameraProjection(camera);
                 var temp = new Matrix4x4();