PUP-2745 Forge malformed dependency fix

Prior to this commit a malformed name in the dependencies for a downloaded forge
module dependency would cause the PMT to fail unexpectedly.
This commit causes the PMT to ignore malformed dependencies.

Depends on https://github.com/puppetlabs/puppet/pull/2827
`#select` and an iterator feels a little weird here, since there's guaranteed to be at most one duplicate.  `#find` will leave a cleaner nesting, and perhaps a clearer path.