MDEV-11464 Server crashes in mark_object upon JSON_VALID.

        Depth of nested objects should be controlled.

mysql-test/r/func_json.result

@@ -13,6 +13,9 @@ json_valid('[false, true, null]')
 select json_valid(repeat('[', 1000));
 json_valid(repeat('[', 1000))
 0
+select json_valid(repeat('{"a":', 1000));
+json_valid(repeat('{"a":', 1000))
+0
 select json_value('{"key1":123}', '$.key2');
 json_value('{"key1":123}', '$.key2')
 NULL

mysql-test/t/func_json.test

@@ -3,6 +3,7 @@ select json_valid('"string"}');
 select json_valid('{"key1":1, "key2":[2,3]}');
 select json_valid('[false, true, null]');
 select json_valid(repeat('[', 1000));
+select json_valid(repeat('{"a":', 1000));
 
 select json_value('{"key1":123}', '$.key2');
 select json_value('{"key1":123}', '$.key1');