test-path-utils: Fix off by one, found by valgrind

When normalizing an absolute path, we might have to add a slash _and_ a
NUL to the buffer, so the buffer was one too small.

Let's just future proof the code and alloc PATH_MAX + 1 bytes.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

test-path-utils.c

@@ -3,7 +3,7 @@
 int main(int argc, char **argv)
 {
 	if (argc == 3 && !strcmp(argv[1], "normalize_absolute_path")) {
-		char *buf = xmalloc(strlen(argv[2])+1);
+		char *buf = xmalloc(PATH_MAX + 1);
 		int rv = normalize_absolute_path(buf, argv[2]);
 		assert(strlen(buf) == rv);
 		puts(buf);