Added fixture [#CLICKHOUSE-3901]

dbms/tests/queries/bugs/nested_merge_multidimensional_array.sql

+DROP TABLE IF EXISTS test.sites;
+CREATE TABLE test.sites (Domain String, `Users.UserID` Array(UInt64), `Users.Dates` Array(Array(Date))) ENGINE = MergeTree ORDER BY Domain SETTINGS vertical_merge_algorithm_min_rows_to_activate = 0, vertical_merge_algorithm_min_columns_to_activate = 0;
+
+SYSTEM STOP MERGES;
+
+INSERT INTO test.sites VALUES ('yandex.ru',[4773498661529650001],[[]]),('yandex.ru',[1936412071529050001],[[]]);
+INSERT INTO test.sites VALUES ('yandex.ru/video',[4773498661529650001],[['2018-06-22']]);
+
+SELECT count(), countArray(Users.Dates), countArrayArray(Users.Dates) FROM test.sites;
+SYSTEM START MERGES;
+OPTIMIZE TABLE test.sites FINAL;
+SELECT count(), countArray(Users.Dates), countArrayArray(Users.Dates) FROM test.sites;
+
+DROP TABLE test.sites;