ogn-decode web server doesn't come up if no DVB stick

[matburnham]

Raising here as there's not a ogn-decode repo...

No major issue as such but while ogn-rf's web server on 8081 comes up when I've not got a dongle plugged in, ogn-decode's on 8080 doesn't. Reason being is that it's looking for /var/run/ogn-decode.fifo but that's not there. Would be nice if the web interface was still able to come up and point this out without having to start digging in via SSH. Or could the ogn-decode web interface be more explicit that something's up that just refusing to offer spectrograms?