Merge pull request #1472 from Unity-Technologies/hdrp/LayeredLit-zero-value-height-blend

Add a minimum value when calculing the height blend factors to avoid …

com.unity.render-pipelines.high-definition/HDRP/Material/LayeredLit/LayeredLitData.hlsl

 
     // Normalize
     maxHeight = GetMaxHeight(maskedHeights);
-    maskedHeights = maskedHeights / maxHeight.xxxx;
+    maskedHeights = maskedHeights / max(maxHeight.xxxx, 1e-6);
 
     return maskedHeights.yzwx;
 }