added catch for empty funding objects

[collinschwantes]

#51

[codecov-commenter]

Codecov Report

❌ Patch coverage is 91.30435% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.21%. Comparing base (6eae5f7) to head (27ecf7d).

Files with missing lines	Patch %	Lines
R/extract_metadata_from_doi.R	91.30%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #52      +/-   ##
==========================================
- Coverage   87.39%   87.21%   -0.18%     
==========================================
  Files          10       10              
  Lines         912      915       +3     
==========================================
+ Hits          797      798       +1     
- Misses        115      117       +2     

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