plex: prevent [] syntax issue (#9318)

Author: MickLesk

ct/plex.sh

@@ -23,7 +23,8 @@ function update_script() {
   header_info
   check_container_storage
   check_container_resources
-  if [ ! -f /etc/apt/sources.list.d/plexmediaserver.list ]] && [[ ! -f /etc/apt/sources.list.d/plexmediaserver.sources ]]; then
+  if [[ ! -f /etc/apt/sources.list.d/plexmediaserver.list ]] \
+   && [[ ! -f /etc/apt/sources.list.d/plexmediaserver.sources ]]; then
     msg_error "No ${APP} Installation Found!"
     exit
   fi