notification: do not allow empty id with --ongoing

Ongoing notifications can only be removed with
termux-notification-remove, which requires the notification id.
An ongoing notification without an id requires a reboot to be removed.
This commit forbids creating such an "unremovable" notification.

Author: xalexalex

scripts/termux-notification

@@ -114,6 +114,12 @@ done
 
 if [ $# != 0 ]; then echo "$SCRIPTNAME: too many arguments"; exit 1; fi
 
+if [ "$OPT_ONGOING" == true ] && [ -z "$OPT_ID" ]; then
+	echo "Ongoing notifications without an ID are not removable."
+	echo "Please set an id with --id \"string\"."
+	exit 1
+fi
+
 set --
 if [ -n "$OPT_ACTION" ]; then set -- "$@" --es action "$OPT_ACTION"; fi
 if [ -n "$OPT_ALERT_ONCE" ]; then set -- "$@" --ez alert-once "$OPT_ALERT_ONCE"; fi