Skip unnecessary toposorting in DEModel._collect_heaviside_roots

[dweindl]

Sorting is only required if roots have been found. Most often this will not be the case. Only sort when necessary.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (3573131) 77.75% compared to head (7e7fb90) 77.75%.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #2299   +/-   ##
========================================
  Coverage    77.75%   77.75%           
========================================
  Files          318      318           
  Lines        20511    20513    +2     
  Branches      1436     1436           
========================================
+ Hits         15948    15950    +2     
  Misses        4560     4560           
  Partials         3        3           

Flag	Coverage Δ
cpp	73.53% <100.00%> (+<0.01%)	⬆️
cpp_python	34.00% <100.00%> (+<0.01%)	⬆️
petab	36.38% <100.00%> (-0.02%)	⬇️
python	72.31% <100.00%> (+<0.01%)	⬆️
sbmlsuite	∅ <ø> (∅)

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Files	Coverage Δ
python/sdist/amici/de_export.py	91.77% <100.00%> (+0.01%)	⬆️