[misc] Apply safe guards and minor improvements

[felixdittrich92]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 72.72727% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.64%. Comparing base (51e1f8a) to head (b8f12ea).

Files with missing lines	Patch %	Lines
doctr/models/predictor/pytorch.py	0.00%	2 Missing ⚠️
doctr/models/builder.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2104      +/-   ##
==========================================
+ Coverage   96.59%   96.64%   +0.04%     
==========================================
  Files         166      166              
  Lines        8702     8702              
==========================================
+ Hits         8406     8410       +4     
+ Misses        296      292       -4     

Flag	Coverage Δ
unittests	96.64% <72.72%> (+0.04%)	⬆️

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