Merge pull request #200 from Unity-Technologies/Branch_FixSkyUpdate

Fixed a problem where the sky reflection probe would be garbage after a domain reload.

Assets/ScriptableRenderPipeline/HDRenderPipeline/Sky/SkyManager.cs

                 Utilities.Destroy(m_SkyboxMarginalRowCdfRT);
                 Utilities.Destroy(m_SkyboxConditionalCdfRT);
 
-                m_UpdateRequired = true; // Special case. Even if update mode is set to OnDemand, we need to regenerate the environment after destroying the texture.
+                m_SkyboxCubemapRT = null;
+                m_SkyboxGGXCubemapRT = null;
+                m_SkyboxMarginalRowCdfRT = null;
+                m_SkyboxConditionalCdfRT = null;
             }
 
             if (m_SkyboxCubemapRT == null)
                     m_SkyboxConditionalCdfRT.filterMode = FilterMode.Point;
                     m_SkyboxConditionalCdfRT.Create();
                 }
+
+                m_UpdateRequired = true; // Special case. Even if update mode is set to OnDemand, we need to regenerate the environment after destroying the texture.
             }
 
             m_CubemapScreenSize = new Vector4((float)resolution, (float)resolution, 1.0f / (float)resolution, 1.0f / (float)resolution);