Hey @refactor-droidyy! Thanks for your first contribution! It's awesome to see new people contributing to our project. 🤗
This changes doesn't fix the error properly, the error is related to this function.
The messages is accessed when we call this function (at the constructor time), so, all access to messages.length inner this function are always returning 0, since it was instantiated once before.
The right solution is access messages state at each fetchFunc, like this:

fetchFunc: async() => {
  const { messages } = this.state;
  const result = await RocketChat.getFiles(this.rid, this.t, messages.length);
   return { ...result, messages: result.files };
}

LGTM