Fix error when too few reads on chromosome

[pontushojer]

fix #7

[codecov]

Codecov Report

Merging #8 (1482f54) into main (2f6ba84) will increase coverage by 0.34%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main       #8      +/-   ##
==========================================
+ Coverage   93.00%   93.34%   +0.34%     
==========================================
  Files          10       10              
  Lines        1400     1413      +13     
  Branches      246      247       +1     
==========================================
+ Hits         1302     1319      +17     
+ Misses         59       57       -2     
+ Partials       39       37       -2     

Files Changed	Coverage Δ
src/naibr/distributions.py	86.66% <100.00%> (+1.81%)	⬆️
src/naibr/get_reads.py	97.53% <100.00%> (+0.98%)	⬆️
tests/test_run.py	100.00% <100.00%> (ø)

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