Fix critical error with new custom Postfix config

install/lib/installer_base.lib.php

@@ -1177,7 +1177,7 @@ class installer_base {
 		}
 		$configfile = 'postfix_custom.conf';
 		if(file_exists($conf['ispconfig_install_dir'].'/server/conf-custom/install/' . $configfile . '.master')) {
-			$content = rfsel($conf['ispconfig_install_dir'].'/server/conf-custom/install/'.$configfile.'.master');
+			$content = file_get_contents($conf['ispconfig_install_dir'].'/server/conf-custom/install/'.$configfile.'.master');
 			$content = strtr($content, $postconf_placeholders);
 			$postconf_commands = array_merge($postconf_commands, array_filter(explode("\n", $content)));
 		}