Init order fix for post process

Author: JulienIgnace-Unity

com.unity.render-pipelines.high-definition/Runtime/PostProcessing/PostProcessSystem.cs

@@ -160,9 +160,6 @@ public PostProcessSystem(HDRenderPipelineAsset hdAsset, RenderPipelineResources
             var postProcessSettings = hdAsset.currentPlatformRenderPipelineSettings.postProcessSettings;
             m_LutSize = postProcessSettings.lutSize;
 
-            // Call after initializing m_LutSize as it's needed for render target allocation.
-            InitializeNonRenderGraphResources(hdAsset);
-
             // Grading specific
             m_HableCurve = new HableCurve();
 
@@ -172,8 +169,6 @@ public PostProcessSystem(HDRenderPipelineAsset hdAsset, RenderPipelineResources
             // TODO: Write a version that uses structured buffer instead of texture to do atomic as Metal doesn't support atomics on textures.
             m_MotionBlurSupportsScattering = m_MotionBlurSupportsScattering && (SystemInfo.graphicsDeviceType != GraphicsDeviceType.Metal);
 
-            FillEmptyExposureTexture();
-
             // Initialize our target pool to ease RT management
             m_Pool = new TargetPool();
 
@@ -192,6 +187,9 @@ public PostProcessSystem(HDRenderPipelineAsset hdAsset, RenderPipelineResources
                 // if only rendering has an alpha channel (and not post-processing), then we just copy the alpha to the output (but we don't process it).
                 m_KeepAlpha = hdAsset.currentPlatformRenderPipelineSettings.supportsAlpha;
             }
+
+            // Call after initializing m_LutSize and m_KeepAlpha as it's needed for render target allocation.
+            InitializeNonRenderGraphResources(hdAsset);
         }
 
         public void Cleanup()
@@ -257,6 +255,8 @@ public void InitializeNonRenderGraphResources(HDRenderPipelineAsset hdAsset)
                 enableRandomWrite: true, name: "Empty EV100 Exposure"
             );
 
+            FillEmptyExposureTexture();
+
             // Misc targets
             m_TempTexture1024 = RTHandles.Alloc(
                 1024, 1024, colorFormat: GraphicsFormat.R16G16_SFloat,