Fixed IndexError when a translation with overridden and unchanged Chooser inside a ListBlock is published

[murray3k]

This affected all Choosers inside a ListBlock , when only one of them is translated and the other kept unchanged.
I added a simple empty check to handle_list_block so that self.handle_block is not called when there are no block_segments , which was causing the IndexError later. This fixes #855.

Added two Tests. One with images in a list where only one is changed and another one for a list with PageChooserBlocks. Might be redundant, but I wanted to test that this issue is with all choosers and not just the PageChooserBlock where we encountered it.

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.18%. Comparing base (0800647) to head (619a676).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #856      +/-   ##
==========================================
+ Coverage   93.13%   93.18%   +0.04%     
==========================================
  Files          47       47              
  Lines        4241     4242       +1     
  Branches      550      551       +1     
==========================================
+ Hits         3950     3953       +3     
+ Misses        174      173       -1     
+ Partials      117      116       -1     

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