Fix the sample index

ScriptableRenderPipeline/Core/ShaderLibrary/ImageBasedLighting.hlsl

         // X = Sum(Radiance(L) * Weight) / Sum(Weight) = Sum(Radiance(L) * F * G) / Sum(F * G).
 
     #ifndef USE_KARIS_APPROXIMATION
-        float F0  = 1; // The choice of the Fresnel factor does not appear to affect the result
-        float F   = F_Schlick(F0, LdotH);
+        // The choice of the Fresnel factor does not appear to affect the result.
+        float F   = 1; // F_Schlick(F0, LdotH);
         float V   = V_SmithJointGGX(NdotL, NdotV, roughness, preLambdaV);
         float G2  = V * NdotL * NdotV; // 4 cancels out
         lightInt += F * G2 * val;

ScriptableRenderPipeline/HDRenderPipeline/Sky/ComputeGgxIblSampleData.compute

 
     while (true)
     {
-        int wastedSampleCount = 0;
+        int acceptedSampleCount = 0;
+        int shiftedSampleIndex  = 0;
 
         for (int i = 0; i < sampleCount; i++)
         {
             SampleVisibleAnisoGGXDir(u, V, k_identity3x3, roughness, roughness, localL, NdotL, NdotH, LdotH, true);
 
-            if (NdotL <= 0) wastedSampleCount++;
+            if (NdotL > 0)
+            {
+                if (acceptedSampleCount == sampleIndex) shiftedSampleIndex = i;
+                acceptedSampleCount++;
+            }
-        if (validSampleCount == sampleCount - wastedSampleCount) break;
+        if (acceptedSampleCount == validSampleCount)
+        {
+            sampleIndex = shiftedSampleIndex;
+            break;
+        }
+
         sampleCount++;
     }