Jeff King authored Apr 10, 2017 and Junio C Hamano committed Apr 16, 2017

Commit e9d9a8a4

 (connect: handle putty/plink also in
GIT_SSH_COMMAND, 2017-01-02) added a call to
split_cmdline(), but checks only for a non-zero return to
see if we got any output. Since the function returns
negative values (and a NULL argv) on error, we end up
dereferencing NULL and segfaulting.

Arguably we could report on the parsing error here, but it's
probably not worth it. This is a best-effort attempt to see
if we are using plink. So we can simply return here with
"no, it wasn't plink" and let the shell actually complain
about the bogus quoting.

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