Overwrite index information if the package doesn't have a information.

I split a Amon2::Plugin::Web::CSRFDefender from Amon2 core distribution.
Older Amon2 core distribution contains A::P::W::CSRFDefender without
version number.
And now, I split A::P::W::CSRFDefender in splitted its own distribution.
It has a version number.
Then, anton should index new A::P::W::CSRFDefender dist.