Only set ParserContext extent to world if null when setting world

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

@@ -131,8 +131,12 @@ public class ParserContext {
      */
     public void setWorld(@Nullable World world) {
         this.world = world;
+        //FAWE start - only set extent to world if null
+        if (extent == null) {
             setExtent(world);
         }
+        //FAWE end
+    }
 
     /**
      * Get the {@link Actor} set on this context.