fix: actually register the listener

src/main/java/ftbsc/geb/GEB.java

@@ -46,6 +46,8 @@ public class GEB implements IBus {
 			listener.getClass(),
 			ConcurrentHashMap.newKeySet()
 		);
+
+		this.listenerMap.get(listener.getClass()).add(listener);
 	}
 
 	/**

src/main/java/ftbsc/geb/api/IBus.java

@@ -21,6 +21,7 @@ public interface IBus {
 	/**
 	 * Tells you whether a listener is currently registered.
 	 * Ideally this should be efficient.
+	 * @param listener the listener to check
 	 * @return true if the listener is registered
 	 */
 	boolean isRegistered(IListener listener);