Fixed checks for height, width, and values to display

[kdiers]

This PR includes two minor fixes for variable names in height, width checking, and restricts checks for values to display to cases where an overlaypath is not None, which would otherwise interfere with e.g. annotation plotting,

[codecov]

Codecov Report

❌ Patch coverage is 0% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 4.97%. Comparing base (5c0a314) to head (2cbfc5e).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
whippersnappy/core.py	0.00%	14 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##            main     #49      +/-   ##
========================================
- Coverage   4.98%   4.97%   -0.01%     
========================================
  Files          6       6              
  Lines        883     884       +1     
  Branches     127     128       +1     
========================================
  Hits          44      44              
- Misses       836     837       +1     
  Partials       3       3              

Flag	Coverage Δ
unittests	4.97% <0.00%> (-0.01%)	⬇️

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