[PATCH] send-email: Avoid empty transfer encoding header

[Aaron Lindsay <aaron@xxxxxxxxxxxxx>]

Fix a small bug introduced by "7a36987ff (send-email: add an auto option
for transfer encoding, 2018-07-14)

I saw the following message when setting --transfer-encoding for a file
with the same encoding:
    $ git send-email --transfer-encoding=8bit example.patch
    Use of uninitialized value $xfer_encoding in concatenation (.) or string
    at /usr/lib/git-core/git-send-email line 1744.

Signed-off-by: Aaron Lindsay <aaron@xxxxxxxxxxxxx>
---
 git-send-email.perl | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/git-send-email.perl b/git-send-email.perl
index 2be5dac33..39c15bcc8 100755
--- a/git-send-email.perl
+++ b/git-send-email.perl
@@ -1834,7 +1834,7 @@ sub apply_transfer_encoding {
 	my $from = shift;
 	my $to = shift;
 
-	return $message if ($from eq $to and $from ne '7bit');
+	return ($message, $to) if ($from eq $to and $from ne '7bit');
 
 	require MIME::QuotedPrint;
 	require MIME::Base64;
-- 
2.19.1