lei q: support vmd for external-only messages

"lei q" now preserves changes per-message keywords across
invocations when it's --output (Maildir or mbox) is reused
(with or without --augment).

In the future, these changes will be monitored via inotify,
EVFILT_VNODE or IMAP IDLE, too.

Unfortunately, this currently prevents "lei import" from ever
importing a message that's in an external.  That will be fixed
in a future change.

1 files changed, 2 insertions, 0 deletions

diff --git a/t/eml.t b/t/eml.t
index ebd45c13..0cf48f22 100644
--- a/t/eml.t
+++ b/t/eml.t
@@ -26,6 +26,8 @@ sub mime_load ($) {
         is($str, "hi\n", '->new modified body like Email::Simple');
         is($eml->body, "hi\n", '->body works');
         is($eml->as_string, "a: b\n\nhi\n", '->as_string');
+        my $empty = PublicInbox::Eml->new("\n\n");
+        is($empty->as_string, "\n\n", 'empty message');
 }
 
 for my $cls (@classes) {