bugfix: initialize lock

YYWebImage/YYWebImageOperation.m

@@ -266,6 +266,7 @@ static void URLInBlackListAdd(NSURL *url) {
     _finished = NO;
     _cancelled = NO;
     _taskID = UIBackgroundTaskInvalid;
+    _lock = [NSRecursiveLock new];
     return self;
 }