dir.c: fix match_pathname()

dir.c: fix match_pathname()

Given the pattern "1/2/3/4" and the path "1/2/3/4/f", the pattern
prefix is "1/2/3/4". We will compare and remove the prefix from both
pattern and path and come to this code

	/*
	 * If the whole pattern did not have a wildcard,
	 * then our prefix match is all we need; we
	 * do not need to call fnmatch at all.
	 */
	if (!patternlen && !namelen)
		return 1;

where patternlen is zero (full pattern consumed) and the remaining
path in "name" is "/f". We fail to realize it's matched in this case
and fall back to fnmatch(), which also fails to catch it. Fix it.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>