video: don't send video-reconfig if video is not initialized

When using --no-video clients would get flooded with video-reconfig events.

I don't know if leaving the mp_notify() call outside of the if was on purpose, but putting it inside fixes the problem above. Maybe there's another fix.

You can reproduce by running e.g. `mpv --input-unix-socket=... --no-video <file>` and then connecting to it using socat.