Avoid reflection in MaskTraverser if possible

worldedit-core/src/main/java/com/boydti/fawe/util/MaskTraverser.java

@@ -2,6 +2,7 @@ package com.boydti.fawe.util;
 
 import com.boydti.fawe.object.mask.ResettableMask;
 import com.sk89q.worldedit.extent.Extent;
+import com.sk89q.worldedit.function.mask.AbstractExtentMask;
 import com.sk89q.worldedit.function.mask.Mask;
 import java.lang.reflect.Field;
 import java.util.Collection;
@@ -26,12 +27,17 @@ public class MaskTraverser {
         }
         Class<?> current = mask.getClass();
         while (current.getSuperclass() != null) {
+            if (mask instanceof AbstractExtentMask) {
+                AbstractExtentMask mask1 = (AbstractExtentMask) mask;
+                mask1.setExtent(newExtent);
+            } else {
                 try {
                     Field field = current.getDeclaredField("extent");
                     field.setAccessible(true);
                     field.set(mask, newExtent);
                 } catch (NoSuchFieldException | IllegalAccessException ignored) {
                 }
+            }
             try {
                 Field field = current.getDeclaredField("mask");
                 field.setAccessible(true);