[PATCH] parser: fix parsing of messages with empty subjects

[Stephen Finucane]

On Sat, 2017-07-08 at 00:24 +1000, Daniel Axtens wrote:
> The fuzz fixups made the test too strict ("if not subject" rather than
> "if subject is None") in an attempt to catch broken subject headers.
> This broke parsing of messages with an empty subject.
> 
> Fix it and add a test.
> 
> Signed-off-by: Daniel Axtens <dja at axtens.net>

Is a mail with an empty subject really valid for our use cases?

Stephen