Merge branch 'v4' of https://gitlab.com/kwoth/nadekobot into v4

docs/guides/windows-guide.md

@@ -32,6 +32,7 @@
 - Click on **`DOWNLOAD`** at the lower right
  ![Bot Setup](https://i.imgur.com/HqAl36p.png "Bot Setup")
 - Click on **`Install`** next to **`Redis`**. 
+- **(Note: Redis is optional unless you are are using the bot on 2000+ servers)**
 - Note: If Redis fails to install, install Redis manually here: [Redis Installer](https://github.com/MicrosoftArchive/redis/releases/tag/win-3.0.504) Download and run the **`.msi`** file.
 - If you will use the music module, click on **`Install`** next to **`FFMPEG`** and **`Youtube-DL`**.
 - If any dependencies fail to install, you can temporarily disable your Windows Defender/AV until you install them. If you don't want to, then read [the last section of this guide](#Manual-Prerequisite-Installation).

src/NadekoBot/Modules/Xp/XpService.cs

@@ -325,7 +325,7 @@ public class XpService : INService, IReadyExecutor, IExecNoCommand
         var user = guild?.GetUser(userId);
         var ch = guild?.GetTextChannel(channelId);
 
-        if (user is null || guild is null)
+        if (guild is null || user is null)
             return;
 
         if (isServer)