Fix "cleared" ellipsoid/cylinder regions still passing isDefined check (#2465)

worldedit-core/src/main/java/com/sk89q/worldedit/regions/selector/CylinderRegionSelector.java

@@ -254,6 +254,8 @@ public class CylinderRegionSelector implements RegionSelector, CUIRegion {
     @Override
     public void clear() {
         region = new CylinderRegion(region.getWorld());
+        selectedCenter = false;
+        selectedRadius = false;
     }
 
     @Override

worldedit-core/src/main/java/com/sk89q/worldedit/regions/selector/EllipsoidRegionSelector.java

@@ -227,6 +227,8 @@ public class EllipsoidRegionSelector implements RegionSelector, CUIRegion {
     public void clear() {
         region.setCenter(BlockVector3.ZERO);
         region.setRadius(Vector3.ZERO);
+        started = false;
+        selectedRadius = false;
     }
 
     @Override