broadcast.go: the checkBroadcastsHandler should ensure disabled broadcasts are stopped

[Trek Hopton]

Currently in performChecksInternalThroughStateMachine if the broadcast is disabled, no checks are performed.

We have observed a case where broadcasts were started, then a new VidGrind version was pushed which disabled the broadcasts. Somehow the state machine and broadcasts were out of sync, the broadcasts were running but disabled. This shouldn’t happen and we should check to make sure that disabled broadcasts aren’t running.

In this case, all rigs ran their broadcasts overnight because they weren’t stopped.