max based on min blend

src/engine/InterestManagement/HeightMap.java

@@ -123,6 +123,8 @@ public class HeightMap {
         int halfExtentsY = (int) Enum.CityBoundsType.ZONE.halfExtents;
         this.zoneLoadID = 0;
         this.seaLevel = 0;
+        this.zone_minBlend = 256;
+        this.zone_maxBlend = 256;
 
         // Cache the full extents to avoid the calculation