Fix issue with 0-sized dispatch with extremely low resolutions (#5272)

* Ceil to int instead.

* changelog

Author: FrancescoC-unity

com.unity.render-pipelines.high-definition/CHANGELOG.md

@@ -344,6 +344,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fixed issue when switching between non-persistent cameras when path tarcing is enabled (case 1337843).
 - Fixed issue with the LayerMaskParameter class storing an erroneous mask value (case 1345515).
 - Fixed issue with vertex color defaulting to 0.0 when not defined, in ray/path tracing (case 1348821).
+- Fix issue with a compute dispatch being with 0 threads on extremely small resolutions.
 
 ### Changed
 - Changed Window/Render Pipeline/HD Render Pipeline Wizard to Window/Rendering/HDRP Wizard

com.unity.render-pipelines.high-definition/Runtime/Lighting/VolumetricLighting/HDRenderPipeline.VolumetricLighting.cs

@@ -516,8 +516,8 @@ TextureHandle GenerateMaxZPass(RenderGraph renderGraph, HDCamera hdCamera, Textu
                             ctx.cmd.SetComputeVectorParam(cs, HDShaderIDs._SrcOffsetAndLimit, srcLimitAndDepthOffset);
                             ctx.cmd.SetComputeFloatParam(cs, HDShaderIDs._DilationWidth, data.dilationWidth);
 
-                            int finalMaskW = maskW / 2;
-                            int finalMaskH = maskH / 2;
+                            int finalMaskW = Mathf.CeilToInt(maskW / 2.0f);
+                            int finalMaskH = Mathf.CeilToInt(maskH / 2.0f);
 
                             dispatchX = HDUtils.DivRoundUp(finalMaskW, 8);
                             dispatchY = HDUtils.DivRoundUp(finalMaskH, 8);