fix: fix adding/getting masks to/from MaskExtent when it is a processor (#2351)

- fixes #2350

worldedit-core/src/main/java/com/fastasyncworldedit/core/util/ProcessorTraverser.java

@@ -0,0 +1,44 @@
+package com.fastasyncworldedit.core.util;
+
+import com.fastasyncworldedit.core.extent.processor.BatchProcessorHolder;
+import com.fastasyncworldedit.core.extent.processor.MultiBatchProcessor;
+import com.fastasyncworldedit.core.queue.IBatchProcessor;
+import com.sk89q.worldedit.internal.util.LogManagerCompat;
+import org.apache.logging.log4j.Logger;
+
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+import java.util.ArrayDeque;
+import java.util.Queue;
+
+public class ProcessorTraverser<T extends IBatchProcessor> {
+
+    private static final Logger LOGGER = LogManagerCompat.getLogger();
+
+    private final T root;
+
+    public ProcessorTraverser(@Nonnull T root) {
+        this.root = root;
+    }
+
+    public <U extends IBatchProcessor> @Nullable U find(Class<U> clazz) {
+        try {
+            Queue<IBatchProcessor> processors = new ArrayDeque<>();
+            IBatchProcessor processor = root;
+            do {
+                if (clazz.isAssignableFrom(processor.getClass())) {
+                    return clazz.cast(processor);
+                } else if (processor instanceof MultiBatchProcessor multiProcessor) {
+                    processors.addAll(multiProcessor.getBatchProcessors());
+                } else if (processor instanceof BatchProcessorHolder holder) {
+                    processors.add(holder.getProcessor());
+                }
+            } while ((processor = processors.poll()) != null);
+            return null;
+        } catch (Throwable e) {
+            LOGGER.error("Error traversing processors", e);
+            return null;
+        }
+    }
+
+}