Handle methods being called on transient mods

Suppose you've got foo/bar/baz.rb that defines Foo::Bar::Baz, but there
is no foo.rb or foo/bar.rb. What happens when you invoke
`Foo.method_that_does_not_exist`? Previously, you'd get a
`NoMethodError` on nil. Now you get a `NameError` as if the constant
resolution failed.