MAINT: Skip the pKa computation instead of raising for non-negative systems

[BvB93]

No description provided.

[codecov]

Codecov Report

Merging #121 (a0621e8) into master (dbf0811) will decrease coverage by 0.03%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master     #121      +/-   ##
==========================================
- Coverage   53.80%   53.77%   -0.04%     
==========================================
  Files          36       36              
  Lines        2888     2890       +2     
==========================================
  Hits         1554     1554              
- Misses       1334     1336       +2     

Impacted Files	Coverage Δ
nanoCAT/ligand_solvation.py	17.80% <33.33%> (+0.24%)	⬆️
nanoCAT/cone_angle.py	94.11% <0.00%> (-0.09%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update dbf0811...a0621e8. Read the comment docs.