diff --no-index: do not forget to run diff_setup_done()

Code inspection by Linus found this.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

diff-lib.c

@@ -298,6 +298,8 @@ int setup_diff_no_index(struct rev_info *revs,
 	revs->diffopt.nr_paths = 2;
 	revs->diffopt.no_index = 1;
 	revs->max_count = -2;
+	if (diff_setup_done(&revs->diffopt) < 0)
+		die("diff_setup_done failed");
 	return 0;
 }