apply: use starts_with() in gitdiff_verify_name()

apply: use starts_with() in gitdiff_verify_name()

Avoid running over the end of line -- a C string whose length is not
known to this function -- by using starts_with() instead of memcmp(3)
for checking if it starts with "/dev/null".  Also simply include the
newline in the string constant to compare against.  Drop a comment that
just states the obvious.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>