error NJS-098 with colons in sql comments since version 6.0.0

using the new thin driver, colons in comments sometimes seem to be taken as introducing a bind parameter:

```sql
select
  1
from
  -- :
  dual
where
  -- :
  1=1
```

results in 
```
NJS-098: 1 positional bind values are required but 0 were provided
```

interestingly, neither of the two colons can be removed, or the error disappears
