Fix Pylint complaints for GLD360-reader.

[sjoro]

This PR fixes some Pylint complaints for GLD360-reader and cleans-up the code. The PR contains no added features and/or major changes in the reader.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.08%. Comparing base (fa56be5) to head (7230cfb).
Report is 379 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2992   +/-   ##
=======================================
  Coverage   96.08%   96.08%           
=======================================
  Files         377      377           
  Lines       55155    55157    +2     
=======================================
+ Hits        52997    52999    +2     
  Misses       2158     2158           

Flag	Coverage Δ
behaviourtests	3.94% <0.00%> (-0.01%)	⬇️
unittests	96.18% <100.00%> (+<0.01%)	⬆️

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[coveralls]

Pull Request Test Coverage Report for Build 11951083562

Details

• 23 of 23 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 96.193%

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Totals
Change from base Build 11936881763:	0.0%
Covered Lines:	53243
Relevant Lines:	55350

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💛 - Coveralls

[mraspaud]

LGTM