scrollController.dispose was called twice

[seoyongl]

I encountered an error when calling chatController.dispose as the example code.

Error Message:
A ScrollController was used after being disposed. Once you have called dispose() on a ScrollController, it can no longer be used

`
void dispose() {

// ChatController should be disposed to avoid memory leaks

_chatController.dispose();         <-- here

super.dispose();

}
`

Because the ChatController and ChatListWidget call scrollController.dispose() twice time.