Fixed PR15355, found by Radford Neal: GetObject would get confused by
a call with a named argument that is a literal R_NilValue (as opposed
to a promise).


git-svn-id: https://svn.r-project.org/R/trunk@63050 00db46b3-68df-0310-9c12-caf00c1e9a41
lengthgets2 was sometimes being called on NULL vectors.

git-svn-id: https://svn.r-project.org/R/trunk@63051 00db46b3-68df-0310-9c12-caf00c1e9a41