fix handling g of duplicate speciesReference

[codecov[bot]]

Codecov Report

Merging #127 (72205cf) into main (f700d96) will increase coverage by 5.01%. The diff coverage is 89.47%.

@@            Coverage Diff             @@
##             main     #127      +/-   ##
==========================================
+ Coverage   89.10%   94.11%   +5.01%     
==========================================
  Files           6        6              
  Lines         312      323      +11     
==========================================
+ Hits          278      304      +26     
+ Misses         34       19      -15     

Impacted Files	Coverage Δ
src/reactions.jl	97.45% <89.47%> (+3.06%)	:arrow_up:

... and 4 files with indirect coverage changes

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[paulflang]

This PR fixes #118

[paulflang]

@ArnoStrouwen can you approve this PR if it fixes the problem with your model?