Fix `rand` for truncated normal with 0 variance

[ararslan]

Fixes #1712 Fixes #1867

[ararslan]

Seems I was beaten to the punch by about 2 years: #1273 🙂

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 85.99%. Comparing base (13029c0) to head (5c79db1).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1721   +/-   ##
=======================================
  Coverage   85.99%   85.99%           
=======================================
  Files         144      144           
  Lines        8666     8670    +4     
=======================================
+ Hits         7452     7456    +4     
  Misses       1214     1214           

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[HakanBrian]

This should also resolve #1867