checking variadic "any" argument in parser - should be array

Hello Tom

you did comment

! <----><------><------> * Non-null argument had better be an array.
The parser doesn't
! <----><------><------> * enforce this for VARIADIC ANY functions
(maybe it should?), so
! <----><------><------> * that check uses ereport not just elog.
! <----><------><------> */

So I moved this check to parser.

It is little bit stricter - requests typed NULL instead unknown NULL,
but it can mark error better and early

Regards

Pavel