fix: fix crash of AgoraVideoView with flutter texture rendering

lib/src/impl/global_video_view_controller.dart

@@ -1,3 +1,4 @@
+import 'dart:async';
 import 'dart:convert';
 
 import 'package:agora_rtc_engine/src/impl/video_view_controller_impl.dart';
@@ -17,6 +18,9 @@ class GlobalVideoViewController {
   int _videoFrameBufferManagerIntPtr = 0;
   int get videoFrameBufferManagerIntPtr => _videoFrameBufferManagerIntPtr;
 
+  final Map<int, Completer<void>> _destroyTextureRenderCompleters = {};
+  bool _isDetachVFBMing = false;
+
   Future<void> attachVideoFrameBufferManager(int irisRtcEngineIntPtr) async {
     if (_videoFrameBufferManagerIntPtr != 0) {
       return;
@@ -35,6 +39,20 @@ class GlobalVideoViewController {
     if (_videoFrameBufferManagerIntPtr == 0) {
       return;
     }
+
+    _isDetachVFBMing = true;
+
+    // Need wait for all `destroyTextureRender` functions are called completed before 
+    // `FreeIrisVideoFrameBufferManager`, if not, the `destroyTextureRender`(call
+    // `IrisVideoFrameBufferManager.DisableVideoFrameBuffer` in native side) and 
+    // `FreeIrisVideoFrameBufferManager` will be called parallelly, which will cause crash.
+    for (final completer in _destroyTextureRenderCompleters.values) {
+      if (!completer.isCompleted) {
+        await completer.future;
+      }
+    }
+    _destroyTextureRenderCompleters.clear();
+
     await irisMethodChannel.invokeMethod(IrisMethodCall(
       'FreeIrisVideoFrameBufferManager',
       jsonEncode({
@@ -89,7 +107,17 @@ class GlobalVideoViewController {
     });
   }
 
+  /// Call `IrisVideoFrameBufferManager.DisableVideoFrameBuffer` in the native side
   Future<void> destroyTextureRender(int textureId) async {
+    _destroyTextureRenderCompleters.putIfAbsent(
+        textureId, () => Completer<void>());
+
     await methodChannel.invokeMethod('destroyTextureRender', textureId);
+
+    _destroyTextureRenderCompleters[textureId]?.complete(null);
+
+    if (!_isDetachVFBMing) {
+      _destroyTextureRenderCompleters.remove(textureId);
+    }
   }
 }