Add check for stat file missing typical week

[mdahlhausen]

Pull request overview

The ComStock 2018 weather files have incomplete .stat files.
This checks that the typical week content is available before trying to access the data.
Without it causes a failure in methods using ComStock weather files.

Pull Request Author

• Method changes or additions
• Added tests for added methods
• Resolved yard documentation errors for new code (ran bundle exec rake doc)
• Resolved rubocop syntax errors for new code (ran bundle exec rake rubocop)
• All new and existing tests passes

Review Checklist

This will not be exhaustively relevant to every PR.

• Perform a code review on GitHub
• All related changes have been implemented: method additions, changes, tests
• Check rubocop errors
• Check yard doc errors
• If fixing a defect, verify by running develop branch and reproducing defect, then running PR and reproducing fix
• If a new feature, test the new feature and try creative ways to break it
• CI status: all green or justified