#400 修复FileCacheQueueScheduler自己设置DuplicateRemover会导致NPE的问题

webmagic-extension/src/main/java/us/codecraft/webmagic/scheduler/FileCacheQueueScheduler.java

@@ -179,6 +179,9 @@ public class FileCacheQueueScheduler extends DuplicateRemovedScheduler implement
 
     @Override
     protected void pushWhenNoDuplicate(Request request, Task task) {
+        if (!inited.get()) {
+            init(task);
+        }
         queue.add(request);
         fileUrlWriter.println(request.getUrl());
     }