This applies the fix for bug #5784 to remaining places where we wish
to reject nulls in user-supplied arrays.  In all these places, there's
no reason not to allow a null bitmap to be present, so long as none of
the current elements are actually null.

I did not change some other places where we are looking at system catalog
entries or aggregate transition values, as the presence of a null bitmap
in such an array would be suspicious.