Discord: Fix if you initially provided an invalid token, corrected th…

…e bot token in discord properties, then did /server reload, and then did /discordbot connect, the bot wouldn't reconnect

MCGalaxy/Modules/Relay/Discord/DiscordBot.cs

@@ -215,6 +215,7 @@ public sealed class DiscordBot : RelayBot {
         }
 
         protected override void OnStop() {
+            socket = null;
             if (api != null) {
                 api.StopAsync();
                 api = null;