parse_object_buffer: correct freeing the buffer

parse_object_buffer: correct freeing the buffer

If we exit early in the function parse_object_buffer, we did not
write to *eaten_p. Then the calling function parse_object, which looks
like the following with respect to the eaten variable, cannot rely on a
proper value set in eaten, hence the freeing of the buffer depends
on random values in memory.

	struct object *parse_object(const unsigned char *sha1)
	{
		int eaten;
		...
		obj = parse_object_buffer(sha1, type, size, buffer, &eaten);
		if (!eaten)
			free(buffer);
	}

This change makes sure, the buffer freeing condition is deterministic.

Signed-off-by: Stefan Beller <stefanbeller@googlemail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>