Search for a space character only within the current line in
read_commit_extra_header_lines() instead of searching in the whole
buffer (and possibly beyond, if it's not NUL-terminated) and then
discarding any results after the end of the current line.
Signed-off-by: Rene Scharfe <l.s.r@web.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>