TTT: Fixes issue with spectating players at prep

If a player spectates during prep they will be spectating that prop if they die before the round restarts. This calls PROPSEC.End on players who currently have a propspec table during the start of a round, it must also be called after aborting is not possible because we don't want to boot people out of spectator when the round isn't going to start anyway.

garrynewman/garrysmod#567