CollectEventArgsAsync in Interactivity causes Null Ref on Dispose

Created by: jeffreyladd

Summary

This was originally reported on Discord by: Pando#7923

After the Global Timeout for Interactivity has been met when using Interactivity#CollectEventArgsAsync a Null Ref is hit within DSharpPlus.Interactivity.EventHandling.CollectRequest.cs within the Dispose Method at this._collected.Clear(); as _collected is already null

Details

Below is the code used to reproduce the Error

[Command("test")]
        public async Task Test(CommandContext ctx)
        {
            var interactivity = ctx.Client.GetInteractivity();

            var users = await interactivity.CollectEventArgsAsync<MessageCreateEventArgs>
                (x => x.Message.Content == "join" && x.Channel == ctx.Channel, TimeSpan.FromSeconds(10))
                .ConfigureAwait(false);

            if (users == null)
            {
                await ctx.RespondAsync("error").ConfigureAwait(false);
            }
            else
            {
                await ctx.RespondAsync(users.Count.ToString()).ConfigureAwait(false);
            }
        }

var icfg = new InteractivityConfiguration()
            {
                Timeout = TimeSpan.FromMinutes(1)
            };

            _interactivity = _client.UseInteractivity(icfg);

Steps to reproduce

1. Launch Bot
2. execute !test command
3. type join
4. Everything finishes correctly
5. After the 1 minute timeout is met from the Global configuration, a null reference is seen as _collected is already null