fetchmail -- null pointer dereference in multidrop mode with headerless email

The fetchmail team reports:

Fetchmail contains a bug that causes an application crash
when fetchmail is configured for multidrop mode and the
upstream mail server sends a message without headers. As
fetchmail does not record this message as “previously fetched”,
it will crash with the same message if it is re-executed, so it
cannot make progress. A malicious or broken-into upstream server
could thus cause a denial of service in fetchmail clients.