Handle unavailable audio node in MusicManager

Added a check for null `getLink()` in `MusicManager` before attempting connection to the audio channel. This ensures users receive a clear error message if the audio node is unavailable, improving error handling and user feedback.

src/main/java/me/bobert/netneutrality/utils/MusicUtils.java

@@ -42,6 +42,11 @@ public class MusicUtils {
         }
 
         if (!checkOnly && manager.isNotConnectedTo(audioChannel)) {
+            if (manager.getLink() == null) {
+                context.reply("The audio node is currently unavailable, please try again later");
+                return false;
+            }
+
             manager.connect(audioChannel);
             manager.getScheduler().attachContext(new MusicChannelContext((GuildMessageChannel) context.getChannel(), context.getGuildUser()));
         }