Fix EllipseMask ignoring center-position when testing

Author: TBlueF

core/src/main/java/de/bluecolored/bluemap/core/map/mask/EllipseMask.java

@@ -58,6 +58,8 @@ public boolean test(int x, int y, int z) {
     }
 
     public boolean testXZ(double x, double z) {
+        x = x - center.getX();
+        z = z - center.getY();
         return (x * x) / radiusSquaredX + (z * z) / radiusSquaredZ <= 1.0;
     }