Fixed sky default light probe when no SkySetting is set.

ScriptableRenderPipeline/HDRenderPipeline/Sky/SkyManager.cs

                 using (new ProfilingSample(cmd, "DynamicGI.UpdateEnvironment"))
                 {
                     // TODO: Properly send the cubemap to Enlighten. Currently workaround is to set the cubemap in a Skybox/cubemap material
+                    float intensity = IsSkyValid() ? 1.0f : 0.0f;
-                    RenderSettings.skybox = IsSkyValid() ? m_StandardSkyboxMaterial : null; // Setup this material as the default to be use in RenderSettings
-                    RenderSettings.ambientIntensity = 1.0f; // fix this to 1, this parameter should not exist!
+                    RenderSettings.skybox = m_StandardSkyboxMaterial; // Setup this material as the default to be use in RenderSettings
+                    RenderSettings.ambientIntensity = intensity; // fix this to 1, this parameter should not exist!
-                    RenderSettings.reflectionIntensity = 1.0f;
+                    RenderSettings.reflectionIntensity = intensity;
                     RenderSettings.customReflection = null;
                     DynamicGI.UpdateEnvironment();