[APV] Fix warning when baking APV with zero occlusion data

Author: pmavridis

Packages/com.unity.render-pipelines.core/Editor/Lighting/ProbeVolume/ProbeGIBaking.Serialization.cs

@@ -1070,7 +1070,11 @@ unsafe static void WriteBakingCells(BakingCell[] bakingCells)
 
             AssetDatabase.ImportAsset(cellDataFilename);
             AssetDatabase.ImportAsset(cellOptionalDataFilename);
-            AssetDatabase.ImportAsset(cellProbeOcclusionDataFilename);
+            // If we did not write a probe occlusion file (because it was zero bytes), don't try to load it (UUM-101480)
+            if (probeOcclusion.Length > 0)
+            {
+                AssetDatabase.ImportAsset(cellProbeOcclusionDataFilename);
+            }
             AssetDatabase.ImportAsset(cellBricksDataFilename);
             AssetDatabase.ImportAsset(cellSharedDataFilename);
             AssetDatabase.ImportAsset(cellSupportDataFilename);