Only set ParserContext extent to world if null when setting world

worldedit-core/src/main/java/com/sk89q/worldedit/extension/input/ParserContext.java

@@ -131,7 +131,11 @@ public class ParserContext {
      */
     public void setWorld(@Nullable World world) {
         this.world = world;
-        setExtent(world);
+        //FAWE start - only set extent to world if null
+        if (extent == null) {
+            setExtent(world);
+        }
+        //FAWE end
     }
 
     /**