Re: [PATCH] git-send-email: don't return undefined value in extract_valid_address()

Krzysztof Mazur [off-list ref] writes:

Yes, it's just to hide the warning, the error (warning in this case) it's
already correctly generated:

W: unable to extract a valid address from: x a.patch

But it is of no use if the message is sent out without the intended
recipient, no?  It is too late when you notice it.

Maybe we should change it to an error?

At least, when we are not giving the "final sanity check [Y/n]?"
prompt, I think the code should error out.