share, transfer-manager: handle a case when all ports are busy

src/mconnect/share.vala

@@ -193,6 +193,10 @@ class ShareHandler : Object, PacketHandlerInterface {
 
 		uint16 port;
 		var listener = Core.instance().transfer_manager.make_listener(out port);
+		if (listener == null) {
+			warning("coult not allodate a listener");
+			return;
+		}
 		debug("allocated listener on port %u", port);
 
 		var t = new UploadTransfer(dev, listener, input, size);

src/mconnect/transfer-manager.vala

@@ -32,7 +32,7 @@ class TransferManager : Object {
 		new_transfer(job);
 	}
 
-	public SocketService make_listener(out uint16 listen_port) {
+	public SocketService? make_listener(out uint16 listen_port) {
 		var ss = new SocketService();
 		for (var port = PORT_MIN; port <= PORT_MAX; port++) {
 			var added = false;
@@ -49,6 +49,7 @@ class TransferManager : Object {
 				return ss;
 			}
 		}
+		ss.close();
 		warning("could not find a free port to listen on");
 		return null;
 	}