diff --stat: status of unmodified pair in diff-q is not zero

It is spelled DIFF_STATUS_UNKNOWN these days, and is different from zero.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff.c

@@ -2411,7 +2411,7 @@ static void builtin_diffstat(const char *name_a, const char *name_b,
 	}
 
 	data = diffstat_add(diffstat, name_a, name_b);
-	data->is_interesting = p->status != 0;
+	data->is_interesting = p->status != DIFF_STATUS_UNKNOWN;
 
 	if (!one || !two) {
 		data->is_unmerged = 1;