send-email: avoid empty transfer encoding header
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.
The new tests are by brian m. carlson.
Signed-off-by: Aaron Lindsay <aaron@aclindsay.com>
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>