Warn zero

[hyanwong]

Fixes #683. Also includes some changes to make the VCF reading code a little more picky.

[codecov]

Codecov Report

Merging #685 (0e3305c) into main (2a06def) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #685   +/-   ##
=======================================
  Coverage   93.10%   93.11%           
=======================================
  Files          17       17           
  Lines        5151     5153    +2     
  Branches      958      959    +1     
=======================================
+ Hits         4796     4798    +2     
  Misses        235      235           
  Partials      120      120           

Flag	Coverage Δ
C	93.11% <100.00%> (+<0.01%)	⬆️
python	96.32% <100.00%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
tsinfer/inference.py	98.57% <100.00%> (+<0.01%)	⬆️

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[jeromekelleher]

LGTM