connect.c: fix leak in handle_ssh_variant

connect.c: fix leak in handle_ssh_variant

When we see an error from split_cmdline(), we exit the
function without freeing the copy of the command string we
made.

This was sort-of introduced by 22e5ae5c8 (connect.c: handle
errors from split_cmdline, 2017-04-10). The leak existed
before that, but before that commit fixed the bug, we could
never trigger this else clause in the first place.

Signed-off-by: Jeff King <redacted>
Signed-off-by: Junio C Hamano <redacted>