Make StructureUploadWidget resilient towards invalid files

[danielhollas]

Fixes #755

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.06%. Comparing base (4676c32) to head (2870a7f).

Files with missing lines	Patch %	Lines
aiidalab_widgets_base/utils/__init__.py	80.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #756      +/-   ##
==========================================
+ Coverage   84.88%   85.06%   +0.17%     
==========================================
  Files          18       18              
  Lines        3388     3388              
==========================================
+ Hits         2876     2882       +6     
+ Misses        512      506       -6     

Flag	Coverage Δ
python-3.12	85.03% <80.00%> (+0.17%)	⬆️
python-3.9	85.05% <80.00%> (+0.17%)	⬆️

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[yakutovicha]

little question