Pipe an empty file to bogofilter with -l and it still
logs "1 messages", e.g.:
Mar 29 19:10:53 thor bogofilter: register-Sn, 0
words, 1 messages
I would expect it to say "0 messages" in this case, or
just exit silently or something.
It doesn't update the message counts in the .db files,
so this is a fairly trivial bug.