Replaced non-error assertion with logger output

src/de/tud/kom/p2psim/impl/transport/modular/ModularTransLayer.java

@@ -260,7 +260,11 @@ public class ModularTransLayer implements SimHostComponent, TransportComponent,
 		 * FIXME add @Override lateron, as soon as the API is updated globally.
 		 */
 		public void removeTransportMessageListener() {
-			assert listener != null;
+			// assert listener != null;
+			if (listener == null) {
+				Monitor.log(ModularTransLayer.class, Level.DEBUG, "Trying tor remove a non-existing transport message listener.");
+				return;
+			}
 			removeTransMsgListener(listener, localPort);
 			listener = null;
 		}