Fix generators' environment handling

[Enchufa2]

See https://groups.google.com/g/simmer-devel/c/l3tEFjaFHrA/m/bRw9o9tKCQAJ

More specifically, see https://groups.google.com/g/simmer-devel/c/l3tEFjaFHrA/m/wny20fbEAQAJ and messages therein.

[codecov]

Codecov Report

Merging #279 (710b41a) into master (1fab5a6) will decrease coverage by 0.07%.
The diff coverage is 81.81%.

@@            Coverage Diff             @@
##           master     #279      +/-   ##
==========================================
- Coverage   99.42%   99.35%   -0.08%     
==========================================
  Files          47       47              
  Lines        2784     2791       +7     
==========================================
+ Hits         2768     2773       +5     
- Misses         16       18       +2     

Impacted Files	Coverage Δ
R/utils.R	95.31% <77.77%> (-2.97%)	⬇️
R/generators.R	100.00% <100.00%> (ø)

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