OS 3.8 HeatExchangerAirToAirSensibleAndLatent methods

Pull request overview

protect against now-fatal use of `setSensible/LatentEffectivessat75Cooling/HeatingAirFlowRate(0)'

[x] Method changes or additions
[ ] Data changes or additions
[ ] Added tests for added methods
[ ] If methods have been deprecated, update rest of code to use the new methods
[ ] Documented new methods using yard syntax
[ ] Resolved yard documentation errors for new code (ran bundle exec rake doc)
[ ] Resolved rubocop syntax errors for new code (ran bundle exec rake rubocop)
[x] All new and existing tests passes
[ ] If the code adds new require statements, ensure these are in core ruby or add to the gemspec

This will not be exhaustively relevant to every PR.

[x] 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