graph API: fix a bug in the rendering of octopus merges

An off by one error was causing octopus merges with 3 parents to not be
rendered correctly.  This regression was introduced by 427fc5.
Signed-off-by: NAllan Caffee <allan.caffee@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

graph.c

@@ -852,7 +852,7 @@ static void graph_output_commit_line(struct git_graph *graph, struct strbuf *sb)
 			graph_output_commit_char(graph, sb);
 			chars_written++;
 
-			if (graph->num_parents > 3)
+			if (graph->num_parents > 2)
 				chars_written += graph_draw_octopus_merge(graph,
 									  sb);
 		} else if (seen_this && (graph->num_parents > 2)) {

t/t4202-log.sh

@@ -342,7 +342,7 @@ cat > expect <<\EOF
 * initial
 EOF
 
-test_expect_failure 'log --graph with merge' '
+test_expect_sucess 'log --graph with merge' '
 	git log --graph --date-order --pretty=tformat:%s |
 		sed "s/ *$//" >actual &&
 	test_cmp expect actual