(PUP-2745) Skip dependencies with malformed dependencies.

Prior to this commit if we encountered a dependent candidate module with a
malformed dependency, we would just ignore the malformed dependency.
This commit changes that behavior to ignore the entire dependent candidate as
an invalid module, this preventing the installation of a module with unknown
dependencies.
Merge pull request #2980 from highb/fix/master/pup-2745_skip_module

(PUP-2745) Skip dependencies with malformed dependencies.