Install systemd service in install script, skip empty audio device

Stop systemd service with SIGINT

extra/gpu-screen-recorder.service

@@ -14,6 +14,7 @@ Environment=REPLAYDURATION=60
 Environment=OUTPUTDIR=%h/Videos
 Environment=MAKEFOLDERS=no
 ExecStart=/bin/sh -c 'AUDIO="${AUDIO_DEVICE:-$(pactl get-default-sink).monitor}"; gpu-screen-recorder -v no -w $WINDOW -c $CONTAINER -q $QUALITY -k $CODEC -ac $AUDIO_CODEC -a "$AUDIO" -f $FRAMERATE -r $REPLAYDURATION -o "$OUTPUTDIR" -mk $MAKEFOLDERS $ADDITIONAL_ARGS'
+KillSignal=SIGINT
 Restart=on-failure
 RestartSec=5s