debian/apt.cron.daily: test for both existance of dbus-send and if dbus-daemon is actually running

debian/apt.cron.daily

@@ -210,7 +210,7 @@ fi
 UPDATE_STAMP=/var/lib/apt/periodic/update-stamp
 if check_stamp $UPDATE_STAMP $UpdateInterval; then
     if apt-get -qq update 2>/dev/null; then
-        if pidof dbus-daemon >/dev/null; then
+        if which dbus-send >/dev/null && pidof dbus-daemon >/dev/null; then
             dbus-send --system / app.apt.dbus.updated boolean:true
         fi
         update_stamp $UPDATE_STAMP