msgmap: mid_insert: use plain "INSERT" to detect duplicates

"INSERT OR IGNORE" still bumps the auto-increment counter in
SQLite, which causes gaps to appear in NNTP article numbering.

This bug appeared in v2 repos where V2Writable may call ->add
repeatedly on the same message.  This bug is apparent with
public-inbox-watch and work-in-progress IMAP watchers which may
rescan and (attempt to) reinsert the same message on mailbox
changes.

Most uses of public-inbox-mda were not affected, unless the
same message is actually delivered multiple times to the mda.
v1 is not affected, either, since deduplication is only based
on Message-ID and msgmap never sees the duplicate.

Reported-by: "Eric W. Biederman" <ebiederm@xmission.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/lib/PublicInbox/Msgmap.pm b/lib/PublicInbox/Msgmap.pm
index 0035c9e3..5a89b85a 100644
--- a/lib/PublicInbox/Msgmap.pm
+++ b/lib/PublicInbox/Msgmap.pm
@@ -126,9 +126,9 @@ sub mid_insert {
         my ($self, $mid) = @_;
         my $dbh = $self->{dbh};
         my $sth = $dbh->prepare_cached(<<'');
-INSERT OR IGNORE INTO msgmap (mid) VALUES (?)
+INSERT INTO msgmap (mid) VALUES (?)
 
-        return if $sth->execute($mid) == 0;
+        return unless eval { $sth->execute($mid) };
         my $num = $dbh->last_insert_id(undef, undef, 'msgmap', 'num');
         $self->num_highwater($num) if defined($num);
         $num;