lei sucks: don't warn or error out on missing dependencies

%INC can hold undef.  This can be hit on a Linux machine missing
Linux::Inotify2.  Loading PublicInbox::KQNotify is attempted and
PublicInbox/KQNotify.pm always exists, causing the `undef' entry
in %INC when it fails to load IO::KQueue.

$ perl -MData::Dumper -I lib \
	-E 'eval { require PublicInbox::KQNotify }; say Dumper(\%INC)'

1 files changed, 1 insertions, 1 deletions

diff --git a/lib/PublicInbox/LeiSucks.pm b/lib/PublicInbox/LeiSucks.pm
index a71158f3..3e945d0b 100644
--- a/lib/PublicInbox/LeiSucks.pm
+++ b/lib/PublicInbox/LeiSucks.pm
@@ -55,7 +55,7 @@ sub lei_sucks {
         my $dig = Digest::SHA->new(1);
         push @out, "public-inbox blob OIDs of loaded features:\n";
         for my $m (grep(m{^PublicInbox/}, sort keys %INC)) {
-                my $f = $INC{$m};
+                my $f = $INC{$m} // next; # lazy require failed (missing dep)
                 $dig->add('blob '.(-s $f)."\0");
                 $dig->addfile($f);
                 push @out, '  '.$dig->hexdigest.' '.$m."\n";