scripts: Update loopback toggle

scripts/loopbacktoggle.sh

 #!/bin/bash
 
-varfile='/home/ztf/scripts/.vars/lbt'
+varfile="${HOME}/.vars/lbt"
+
+_exit_because_monitor() {
+    mpv /usr/share/sounds/freedesktop/stereo/dialog-error.oga > /dev/null &
+    notify-send -t 1000 -u critical "default source is a monitor?"
+    exit 1
+}
+pactl get-default-source | grep -i "monitor" && _exit_because_monitor
 
 if [[ $(cat "${varfile}") == *on* ]]; then
   echo -n 'off' > "${varfile}"