change assertion to warning

[skjerns]

No description provided.

[codecov]

Codecov Report

Merging #180 (f0f45b5) into master (902e956) will increase coverage by 0.07%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #180      +/-   ##
==========================================
+ Coverage   78.14%   78.21%   +0.07%     
==========================================
  Files           4        4              
  Lines         828      831       +3     
  Branches      180      182       +2     
==========================================
+ Hits          647      650       +3     
  Misses        144      144              
  Partials       37       37              

Flag	Coverage Δ
unittests	78.21% <100.00%> (+0.07%)	⬆️

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Impacted Files	Coverage Δ
pyedflib/highlevel.py	73.91% <100.00%> (+0.28%)	⬆️

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