cherry-pick will segfault when transplanting a root commit if the --ff
option is used. This happens because the "parent" pointer is set to NULL
when the commit being cherry-picked has no parents. Later, when "parent"
is dereferenced, the cherry-pick segfaults.
Fix this by checking whether "parent" is NULL before dereferencing it and
add a test for this case of cherry-picking a root commit with --ff.
Reported-by: Zbyszek Szmek <zbyszek@in.waw.pl>
Signed-off-by: Brandon Casey <casey@nrlssc.navy.mil>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
