Merge pull request #1083 from Unity-Technologies/Branch_FixTessAmplitudeZero

Fixed heightmap offset when amplitude is zero.

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Editor/Material/Lit/LitUI.cs

                     float amplitude = (heightMax[layerIndex].floatValue - heightMin[layerIndex].floatValue);
 
                     heightAmplitude[layerIndex].floatValue = amplitude * 0.01f; // Conversion centimeters to meters.
-                    heightCenter[layerIndex].floatValue = -(heightMin[layerIndex].floatValue + offset) / amplitude;
+                    heightCenter[layerIndex].floatValue = -(heightMin[layerIndex].floatValue + offset) / Mathf.Max(1e-6f, amplitude);
-                    heightCenter[layerIndex].floatValue = -heightOffset[layerIndex].floatValue / amplitude + heightTessCenter[layerIndex].floatValue;
+                    heightCenter[layerIndex].floatValue = -heightOffset[layerIndex].floatValue / Mathf.Max(1e-6f, amplitude) + heightTessCenter[layerIndex].floatValue;
                 }
             }
         }