Fix number of points to draw

[at-wat]

I don't remember why there were -1

This caused wrong points deletion/labeling result when the number of the points are larger than maxDrawArraysPoints

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 38.16%. Comparing base (21954bf) to head (3911faa).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #289   +/-   ##
=======================================
  Coverage   38.16%   38.16%           
=======================================
  Files           8        8           
  Lines        1643     1643           
=======================================
  Hits          627      627           
  Misses        980      980           
  Partials       36       36           

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[f-fl0]

LGTM