Merge branch 'jc/send-email-pre-process-fix'

When "git send-email" that uses the validate hook is fed a message without and then with Message-ID, it failed to auto-assign a unique Message-ID to the former and instead reused the Message-ID from the latter, which has been corrected. This was a fix for a recent regression caught before the release, so no need to mention it in the release notes. * jc/send-email-pre-process-fix: t9001: mark the script as no longer leak checker clean send-email: clear the $message_id after validation