Do not panic if no addresses were found

mtglib/internal/dc/updater.go

 		for {
 			u.logger.Info("start update")
 			if err := callback(); err != nil {
-				u.logger.WarningError("cannot update: %w", err)
+				u.logger.WarningError("cannot update", err)
 			}
 			u.logger.Info("updated")
 

mtglib/proxy.go

 	if err != nil {
 		return fmt.Errorf("no addresses to call: %w", err)
 	}
+	if conn == nil {
+		return fmt.Errorf("no available addresses for DC %d", ctx.dc)
+	}
 
 	tgConn, err := foundAddr.Obfuscator.SendHandshake(conn, ctx.dc)
 	if err != nil {