连续push多个flutter页面时白屏问题修复

ios/Classes/container/FLBFlutterViewContainer.m

@@ -187,6 +187,8 @@ static NSUInteger kInstanceCounter = 0;
  
     [super viewWillAppear:animated];
     [self.view setNeedsLayout];
+    
+    [self surfaceUpdated:YES];
     //instead of calling [super viewWillAppear:animated];, call super's super
 //    struct objc_super target = {
 //        .super_class = class_getSuperclass([FlutterViewController class]),