Conversion failure in v5.20.0

[avandecreme]

When running ./examples/c/convertSBML on this unzipped file I get the following error in v5.20.0:

Attempting to convert model to SBML Level 3 Version 2.
Unable to perform conversion due to the following:
line 4950: (01010 [Error]) Duplicate XML attribute.

Conversion skipped.  Either libSBML does not (yet) have
ability to convert this model, or (automatic) conversion
is not possible in this case.

It is working fine in v5.19

Here is the line 4950 mentioned:
<math xmlns="http://www.w3.org/1998/Math/MathML" xmlns:sbml="http://www.sbml.org/sbml/level3/version1/core">

I suspect the issue is introduced by #310 and more specifically the following lines which copy existing namespaces without checking for collision with the one added a few lines above:
https://github.com/sbmlteam/libsbml/pull/310/files#diff-a1350eea6646b5dc5f2a33f27c7fed1ccb413304f0d4a6df3909a2f0ec15f0c2R2232-R2245