Add a check before toggeling wm

Currently on 1.5.1, sway is not installed nor setted up. This WM toggle
entry cause a tty soft lock !

This fix this with a very too simple check but that will prevent this
case.

scripts/core/sxmo_wmtoggle.sh

@@ -1,11 +1,18 @@
 #!/bin/sh
 
+not_ready_yet() {
+	notify-send "Your device looks not ready yet"
+	exit 1
+}
+
 case "$(realpath /var/lib/tinydm/default-session.desktop)" in
 	/usr/share/wayland-sessions/swmo.desktop)
+		command -v dwm || not_ready_yet
 		sudo tinydm-set-session -f -s /usr/share/xsessions/sxmo.desktop
 		pkill sway
 		;;
 	/usr/share/xsessions/sxmo.desktop)
+		command -v sway || not_ready_yet
 		sudo tinydm-set-session -f -s /usr/share/wayland-sessions/swmo.desktop
 		pkill dwm
 		;;