[PATCH] mbox: do not try to create filename from empty string

[Eric Wong <e@80x24.org>]

This was causing warnings to pop up in syslogs for messages with
empty Subject headers.
---
 lib/PublicInbox/Mbox.pm   | 2 +-
 lib/PublicInbox/MboxGz.pm | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/PublicInbox/Mbox.pm b/lib/PublicInbox/Mbox.pm
index 42cedd15..c50a118b 100644
--- a/lib/PublicInbox/Mbox.pm
+++ b/lib/PublicInbox/Mbox.pm
@@ -18,7 +18,7 @@ use Email::MIME::Encode;
 sub subject_fn ($) {
 	my ($hdr) = @_;
 	my $fn = $hdr->header('Subject');
-	return 'no-subject' unless defined($fn);
+	return 'no-subject' if (!defined($fn) || $fn eq '');
 
 	# no need for full Email::MIME, here
 	if ($fn =~ /=\?/) {
diff --git a/lib/PublicInbox/MboxGz.pm b/lib/PublicInbox/MboxGz.pm
index 1621cff8..ef560426 100644
--- a/lib/PublicInbox/MboxGz.pm
+++ b/lib/PublicInbox/MboxGz.pm
@@ -23,7 +23,7 @@ sub response {
 	my $body = $class->new($ctx, $cb);
 	# http://www.iana.org/assignments/media-types/application/gzip
 	my @h = qw(Content-Type application/gzip);
-	if ($fn) {
+	if (defined $fn && $fn ne '') {
 		$fn = to_filename($fn);
 		push @h, 'Content-Disposition', "inline; filename=$fn.mbox.gz";
 	}