Omit or discount empty recordings

[mcdemarco]

There was a streak of empty recordings from last night's "Armory" pub sing. Ideally they shouldn't count against the last 20 recordings count since they're taking up no server space:

While I was at part of the pub sing, I didn't notice the empty recordings then so I don't know whether they're an additional bug.

[jeffkaufman]

Right now creating a bunch of empty recordings is the only way to scrub the server of your recordings if you don't want to keep them around (#234) so unless I'm going to fix that I shouldn't fix this either.

This is a bit https://xkcd.com/1172/ but oh well