Possibly expand the variable name's embedded variables before using it, as

Possibly expand the variable name's embedded variables before using it, as
seen (somewhat) in NetBSD.  This catches a few extra recursion cases that
could be hidden by expanding a NIL variable causing an existing variable to
be returned (which caused infinite looping and climbing memory usage in at
least one case).

Taken-From: FreeBSD/1.27,1.28 (jmallett), originally obtained from NetBSD