AppendAsColumn doesn't work with Array of Decimals

[astiunov]

There is a minimal example: https://pastebin.com/RJmKpZ33, which works if you replace ColumnDecimal with ColumnDate or ColumnInt64 for a example.

The second assert fails, because AppendAsColumn calls this method. ColumnDecimal isn't inherited from ColumnVector, so the check there fails.

[Enmk]

Fixed in #161, see Unit test here:
https://github.com/ClickHouse/clickhouse-cpp/blob/master/ut/columns_ut.cpp#L956