Correctly detect ZI when there is no ziformula

[strengejacke]

No description provided.

[codecov]

Codecov Report

Merging #830 (4e67384) into main (8e81cc4) will not change coverage.
The diff coverage is 100.00%.

❗ Current head 4e67384 differs from pull request most recent head b04038a. Consider uploading reports for the commit b04038a to get more accurate results

@@           Coverage Diff           @@
##             main     #830   +/-   ##
=======================================
  Coverage   55.04%   55.04%           
=======================================
  Files         124      124           
  Lines       15388    15388           
=======================================
  Hits         8470     8470           
  Misses       6918     6918           

Files	Coverage Δ
R/model_info.R	56.15% <100.00%> (ø)