Fix #817 Check that __open_links exists before trying to close links

[oruebel]

Motivation

Fix #817

How to test the behavior?

This should fix the issue but I'm not sure yet how to test it.

Checklist

• Did you update CHANGELOG.md with your changes?
• Have you checked our Contributing document?
• Have you ensured the PR clearly describes the problem and the solution?
• Is your contribution compliant with our coding style? This can be checked running flake8 from the source directory.
• Have you checked to ensure that there aren't other open Pull Requests for the same change?
• Have you included the relevant issue number using "Fix #XXX" notation where XXX is the issue number? By including "Fix #XXX" you allow GitHub to close issue #XXX when the PR is merged.

[codecov]

Codecov Report

Base: 87.77% // Head: 87.80% // Increases project coverage by +0.02% 🎉

Coverage data is based on head (8c958e8) compared to base (4d3f724).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #818      +/-   ##
==========================================
+ Coverage   87.77%   87.80%   +0.02%     
==========================================
  Files          44       44              
  Lines        8936     8943       +7     
  Branches     2061     2061              
==========================================
+ Hits         7844     7852       +8     
  Misses        777      777              
+ Partials      315      314       -1     

Impacted Files	Coverage Δ
src/hdmf/backends/hdf5/h5tools.py	82.43% <100.00%> (+0.25%)	⬆️

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[rly]

Looks good to me. Please fix flake8 and update the changelog for a bugfix release set for tomorrow or Friday.

[oruebel]

Please fix flake8 and update the changelog

I updated the changelog.

Re flake8, it looks like the GitHub workflows are flaky. Several failed with errors along the lines of:

[oruebel]

@rly I removed the warnings as you suggested in #817 (comment) This PR is ready for review