fixes #4915 - content view publish - resolve method undefined errors

This commit addresses a couple of undefined method errors that
have been observed.

- package_clause_generator - observed error in production configuration
  when filter contained errata; however, same should occur for package
  groups
- content_view_erratum_filter - observed error if the errata id filter
  was empty (ie. no rules/ids)
Merge pull request #3905 from bbuckingham/issue-4915

fixes #4915 - content view publish - resolve method undefined errors