Correct function selection in topoaa when order=0 and limit is used (or not)

[joaomcteixeira]

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• No limit of 20 molecules for topoaa #261 introduced the limit parameter, for which topoaa started handling the models differently depending on the value of limit
• Recently, a lapse in Improve running topoaa as an intermediate step in the workflow #498 introduced a bug in which if order=0 and not limit, the mol_params_get function is not defined.
• This PR solves this bug by correcting the if-block defining the mol_params_get function.

[codecov-commenter]

Codecov Report

Merging #500 (22044c2) into main (e81d302) will increase coverage by 0.01%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main     #500      +/-   ##
==========================================
+ Coverage   72.36%   72.37%   +0.01%     
==========================================
  Files          96       96              
  Lines        6203     6202       -1     
==========================================
  Hits         4489     4489              
+ Misses       1714     1713       -1     

Impacted Files	Coverage Δ
src/haddock/modules/topology/topoaa/__init__.py	44.06% <0.00%> (+0.37%)	⬆️

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