fixed problem in view over view setup (BUG#7433)

mysql-test/r/view.result:
  view over other view setup
mysql-test/t/view.test:
  view over other view setup
sql/table.cc:
  before using ancestor, check that it exists

mysql-test/r/view.result

@@ -1750,3 +1750,11 @@ c1
 1
 drop view v2, v1;
 drop table t1, t2;
+CREATE TABLE t1 (C1 INT, C2 INT);
+CREATE TABLE t2 (C2 INT);
+CREATE VIEW v1 AS SELECT C2 FROM t2;
+CREATE VIEW v2 AS SELECT C1 FROM t1 LEFT OUTER JOIN v1 USING (C2);
+SELECT * FROM v2;
+C1
+drop view v2, v1;
+drop table t1, t2;

mysql-test/t/view.test

@@ -1679,3 +1679,14 @@ select * from v1;
 select * from v2;
 drop view v2, v1;
 drop table t1, t2;
+
+#
+# view over other view setup (BUG#7433)
+#
+CREATE TABLE t1 (C1 INT, C2 INT);
+CREATE TABLE t2 (C2 INT);
+CREATE VIEW v1 AS SELECT C2 FROM t2;
+CREATE VIEW v2 AS SELECT C1 FROM t1 LEFT OUTER JOIN v1 USING (C2);
+SELECT * FROM v2;
+drop view v2, v1;
+drop table t1, t2;

sql/table.cc

@@ -1613,7 +1613,7 @@ void st_table_list::set_ancestor()
     tbl->table->grant= grant;
   }
   /* if view contain only one table, substitute TABLE of it */
-  if (!ancestor->next_local)
+  if (ancestor && !ancestor->next_local)
   {
     table= ancestor->table;
     schema_table= ancestor->schema_table;