send-email: use lexical filehandle for opendir

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.comReviewed-by: Avery Pennarun <apenwarr@gmail.com>
Reviewed-by: Jeff King <peff@peff.net>
>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-send-email.perl

@@ -512,12 +512,12 @@ ($)
 		push @rev_list_opts, "--", @ARGV;
 		@ARGV = ();
 	} elsif (-d $f and !check_file_rev_conflict($f)) {
-		opendir(DH,$f)
+		opendir my $dh, $f
 			or die "Failed to opendir $f: $!";
 
 		push @files, grep { -f $_ } map { catfile($f, $_) }
-				sort readdir(DH);
-		closedir(DH);
+				sort readdir $dh;
+		closedir $dh;
 	} elsif ((-f $f or -p $f) and !check_file_rev_conflict($f)) {
 		push @files, $f;
 	} else {