in case some type's deps are empty

we check $require->{requires} to determine if the structure of $require is
like { requires => { 'Foo' => '1.0' }, build_requires => { 'Bar' => '1.0' } }
or { Foo => '1.0', Bar => '1.0' }, without this fix, we might be wrong about
the structure.
release 2.4.38
bump to 2.4.39