avoid length in boolean context

Perl does not currently optimize for this.

ref (from p5p):
http://mid.gmane.org/D5C27970-9176-4C7A-8B99-7D78360E67A2@pobox.com

1 files changed, 2 insertions, 2 deletions

diff --git a/public-inbox-mda b/public-inbox-mda
index c4822b61..b1f33af5 100755
--- a/public-inbox-mda
+++ b/public-inbox-mda
@@ -64,7 +64,7 @@ if (PublicInbox::MDA->precheck($filter, $dst->{address}) &&
 } else {
         # Ensure emergency spam gets spamassassin headers.
         # This makes it easier to prioritize obvious spam from less obvious
-        if (defined($filtered) && length($filtered)) {
+        if (defined($filtered) && $filtered ne '') {
                 my $drop = Email::MIME->new(\$filtered);
                 $filtered = undef;
                 $filter->simple($drop);
@@ -82,7 +82,7 @@ sub do_spamc {
                 run([qw/spamc -E --headers/], \$orig, $out);
         };
 
-        return ($@ || $? || !defined($$out) || length($$out) == 0) ? 0 : 1;
+        return ($@ || $? || !defined($$out) || $$out eq '') ? 0 : 1;
 }
 
 sub search_index_sync {