Bugfix #2208 ensemble_stat with missing members

[hsoh-u]

Expected Differences

MET builds 8 ensemble members for PRMSL and 10 members for VIS when the input ensemble list contains the missing members. But last two members for VIS are empty list (no data). I'm not sure the design for missing members.
The fix is just checking if member data is available.
The other solution would be:

• Filling with missing values (by adding 2 missing members for PRMSL - make same 10 members for VIS and PRMSL)

• Removing 2 empty members for VIS (make same 8 members for VIS and PRMSL)

• Do these changes introduce new tools, command line arguments, or configuration file options? [No]
  
  If yes, please describe:
  

• Do these changes modify the structure of existing or add new output data types (e.g. statistic line types or NetCDF variables)? [No]
  
  If yes, please describe:
  

Pull Request Testing

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Run /d1/personal/hsoh/data/MET-2208/run.sh where "ensemble_stat" executable exists at seneca

• Recommend testing for the reviewer(s) to perform, including the location of input datasets, and any additional instructions:
  

• Do these changes include sufficient documentation updates, ensuring that no errors or warnings exist in the build of the documentation? [No]

• Do these changes include sufficient testing updates? [No]

• Will this PR result in changes to the test suite? [No]
  
  If yes, describe the new output and/or changes to the existing output:
  

• Please complete this pull request review by [Fill in date].
  

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[georgemccabe]

The change here is a quick fix that Howard and I discussed should fix the issue. However, I will defer to @JohnHalleyGotway since he is more familiar with the code and may have a suggestion for a more robust fix.

[JohnHalleyGotway]

I approve of this change. Thanks for tracking it down @hsoh!

I'll rely on the testing you and @georgemccabe to confirm that what had been broken now works. I do see that GHA ran without error and flagged no differences.

I reviewed the logic of the code change and see that it makes sense.