RaP: Improve check for record events in archive, sanity scripts

There's some cases where you can get 0-duration recordings due to
recording event placement (e.g. a single recording event is the last
event in the events.xml). Detect these cases, and treat them like
no recording marks in the archive script (it will stop the recording
from being automatically processed).

I've also adjusted the sanity script to detect these cases and error
out. The recording processing scripts cannot handle 0-length recordings,
you have to manually edit the events. I've added a message to the
sanity log about this.