fix preDownload event null point exception

Flutter/android/src/main/java/com/tencent/vod/flutter/FTXDownloadManager.java

@@ -72,7 +72,7 @@ public class FTXDownloadManager implements MethodChannel.MethodCallHandler, ITXV
 
                         @Override
                         public void onError(int taskID, String url, int code, String msg) {
-                            onErrorEvent(taskID, url, msg);
+                            onErrorEvent(taskID, url, code, msg);
                         }
                     });
             result.success(retTaskID);
@@ -141,9 +141,10 @@ public class FTXDownloadManager implements MethodChannel.MethodCallHandler, ITXV
         sendSuccessEvent(CommonUtil.getParams(FTXEvent.EVENT_PREDOWNLOAD_ON_COMPLETE, bundle));
     }
 
-    private void onErrorEvent(int taskId, String url, String msg) {
+    private void onErrorEvent(int taskId, String url, int code, String msg) {
         Bundle bundle = new Bundle();
         bundle.putInt("taskId", taskId);
+        bundle.putInt("code", code);
         bundle.putString("url", url);
         bundle.putString("msg", msg);
         sendSuccessEvent(CommonUtil.getParams(FTXEvent.EVENT_PREDOWNLOAD_ON_ERROR, bundle));

Flutter/ios/Classes/FTXDownloadManager.m

@@ -174,7 +174,7 @@
     NSMutableDictionary *dict = [NSMutableDictionary dictionary];
     [dict setObject:@(taskID) forKey:@"taskId"];
     [dict setObject:url forKey:@"url"];
-    [dict setObject:@(error.code) forKey:@"code"];
+    [dict setObject:error.code forKey:@"code"];
     if (nil != error.userInfo.description) {
         [dict setObject:error.userInfo.description forKey:@"msg"];
     }

Flutter/lib/Core/txvoddownload_controller.dart

@@ -145,17 +145,17 @@ class TXVodDownloadController {
     int eventCode = map["event"];
     switch (eventCode) {
       case TXVodPlayEvent.EVENT_PREDOWNLOAD_ON_COMPLETE:
-        int taskId = map['taskId'] as int;
-        String url = map['url'] as String;
+        int taskId = map['taskId'];
+        String url = map['url'];
         LogUtils.d(TAG, 'receive EVENT_PREDOWNLOAD_ON_COMPLETE, taskID=${taskId} ,url=${url}');
         if (_onPreDownloadOnCompleteListener != null) {
           _onPreDownloadOnCompleteListener!(taskId, url);
         }
         break;
       case TXVodPlayEvent.EVENT_PREDOWNLOAD_ON_ERROR:
-        int taskId = map['taskId'] as int;
-        String url = map['url'] as String;
-        int code = map['code'] as int;
+        int taskId = map['taskId'];
+        String url = map['url'];
+        int code = map['code'] ?? 0;
         String msg = map['msg'] ?? '';
         LogUtils.d(TAG, 'receive EVENT_PREDOWNLOAD_ON_ERROR, taskID=${taskId} ,url=${url}, code=${code} , msg=${msg}');
         if (_onPreDownloadOnErrorListener != null) {