[FIX] HeaderView: Do nothing in initStyleOptionForIndex if model is None

[ales-erjavec]

Issue

Fix error in initStyleOptionForIndex:

Traceback (most recent call last):
  File "/Users/aleserjavec/devel/orange3/Orange/widgets/data/owtable.py", line 83, in sectionSizeFromContents
    super().initStyleOptionForIndex(opt, logicalIndex)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^
  File "/Users/aleserjavec/devel/orange3/Orange/widgets/utils/headerview.py", line 105, in initStyleOptionForIndex
    textAlignment = model.headerData(logicalIndex, self.orientation(),
                    ^^^^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'headerData'

This happens during test tear down with Qt 6.8.2

Description of changes

Do nothing in initStyleOptionForIndex if model is None

Includes

• Code changes
• Tests
• Documentation

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 89.02%. Comparing base (a3a3197) to head (58079c3).
⚠️ Report is 2 commits behind head on master.

❌ Your patch status has failed because the patch coverage (66.66%) is below the target coverage (95.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7216      +/-   ##
==========================================
- Coverage   89.02%   89.02%   -0.01%     
==========================================
  Files         335      335              
  Lines       74218    74220       +2     
==========================================
- Hits        66076    66074       -2     
- Misses       8142     8146       +4     

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