make <expr> always overload if expr is overloaded

make <expr> always overload if expr is overloaded

Due to the way that '<> as glob' was parsed differently from
'<> as filehandle' from 5.6 onwards, something like <$foo[0]>
didn't handle overloading, even where $foo[0] was an overloaded object.
This was contrary to the docs for overload, and meant that <> couldn't
be used as a general overloaded iterator operator.