FIX: use datastore._group instead of variable["sweep_number"]

[kmuehlbauer]

• Closes KeyError: 'sweep_data' when opening sigmet file #121
• Tests added
• Changes are documented in history.md

[codecov]

Codecov Report

Merging #123 (2670a5e) into main (1e09e4f) will decrease coverage by 0.03%.
Report is 2 commits behind head on main.
The diff coverage is 85.71%.

@@            Coverage Diff             @@
##             main     #123      +/-   ##
==========================================
- Coverage   88.18%   88.15%   -0.03%     
==========================================
  Files          19       19              
  Lines        3335     3336       +1     
==========================================
  Hits         2941     2941              
- Misses        394      395       +1     

Flag	Coverage Δ
unittests	88.15% <85.71%> (-0.03%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
xradar/io/backends/iris.py	84.77% <66.66%> (-0.09%)	⬇️
xradar/io/export/odim.py	96.77% <100.00%> (ø)

[kmuehlbauer]

@aladinor The approach here reads empty/corrupted sweep from your file and also displays a warning message.

[aladinor]

Thanks @kmuehlbauer for your help!