You can have a detailled description on the change between JMS 1.1.17 and 1.1.19 in the FAQ
www.jms2win.com/faq/change-history-v11x
I don't see why you have a patch to perform on the slave configuration.php file.
Normally, there is not patch for the slave and only for the master configuration.php file.
In addition, the patch was already required in JMS 1.1.17 and I don't see particular changes on this part between JMS 1.1.17 and 1.1.19.
The slave configuration.php files are stored in the /multisites/xxx directory or in the deployed directory.
Concerning the master "configuration.php" files, there are backup at the installation time in the administrator\components\com_multisites\backup_on_install and backup
In those directory, you will find the backup of all the files before the patches.