Fix hashindex .iteritems (1.4-maint)

[ThomasWaldmann]

Description

Fix .iteritems methods to correctly check hashindex_get return value, fixes #9368.

Also tests and cosmetic consistency fixes.

Checklist

• PR is against 1.4-maint branch, only applicable there
• New code has tests and docs where appropriate
• Tests pass (run tox or the relevant test subset)
• Commit messages are clean and reference related issues

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.60%. Comparing base (bc370ee) to head (c5a7a3c).
⚠️ Report is 7 commits behind head on 1.4-maint.

Additional details and impacted files

@@              Coverage Diff              @@
##           1.4-maint    #9370      +/-   ##
=============================================
- Coverage      80.61%   80.60%   -0.01%     
=============================================
  Files             38       38              
  Lines          11260    11260              
  Branches        1771     1771              
=============================================
- Hits            9077     9076       -1     
  Misses          1615     1615              
- Partials         568      569       +1     

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