Merge pull request CoderMJLee#497 from xiaozi4624/master

修复当前正在刷新中时调用beginRefreshing方法使得header insert回置失败

Author: CoderMJLee

MJRefresh/Base/MJRefreshComponent.m

@@ -144,9 +144,12 @@ - (void)beginRefreshing
     if (self.window) {
         self.state = MJRefreshStateRefreshing;
     } else {
-        self.state = MJRefreshStateWillRefresh;
-        // 刷新(预防从另一个控制器回到这个控制器的情况，回来要重新刷新一下)
-        [self setNeedsDisplay];
+        // 预发当前正在刷新中时调用本方法使得header insert回置失败
+        if (self.state != MJRefreshStateRefreshing) {
+            self.state = MJRefreshStateWillRefresh;
+            // 刷新(预防从另一个控制器回到这个控制器的情况，回来要重新刷新一下)
+            [self setNeedsDisplay];
+        }
     }
 }