Empty weather folder trips up run_analysis.rb

[willf]

Pull Request Description

Closes NREL#1176.

Checklist

Not all may apply:

• Tests (and test files) have been updated
• Documentation has been updated
  • If related to resstock-estimation, checklist includes data dictionary, source report, options saturation, options_lookup.
• Changelog has been updated
• openstudio tasks.rb update_measures has been run
• No unexpected regression test changes on CI (checked comparison artifacts)

_{Source: NREL on 2023-12-06.}