Fixing type problem for '#get-REC'/2

When running dialyzer for an empty record, the type for '#get-REC' was wrong.

The return type was the union of all possible field value types. But, the union of no
return values was the empty list, and this is wrong. It is always OK though to
use the following type for the list case.

-spec '#get-REC'([any()], …) -> [any()].

This might be a little bit to general. But, the old one was also general as the input type
already was [any()].

So Ulf - you decide if this is OK.