Fix ck2yaml handling of unnamed surfaces

[speth]

Changes proposed in this pull request

• Fix ck2yaml's handling of surface phase definitions that don't provide a name

If applicable, fill in the issue number this pull request is fixing

Closes #1845

Checklist

• The pull request includes a clear description of this code change
• Commit messages have short titles and reference relevant issues
• Build passes (scons build & scons test) and unit tests address code coverage
• Style & formatting of contributed code follows contributing guidelines
• The pull request is ready for review

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.36%. Comparing base (3f2057c) to head (61ca326).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1876   +/-   ##
=======================================
  Coverage   74.36%   74.36%           
=======================================
  Files         443      443           
  Lines       55407    55407           
  Branches     9105     9105           
=======================================
+ Hits        41201    41203    +2     
+ Misses      11108    11107    -1     
+ Partials     3098     3097    -1     

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