CAST('0', 'DateTime') fails but '00000' works

https://fiddle.clickhouse.com/16f87a7e-0ff0-4b50-ace8-2c8087567b01

and it must specifically be 5 or more 0's in the string

```sql
SELECT CAST('00000', 'DateTime'); -- works
SELECT CAST('0', 'DateTime'); -- fails
```
