fix: panic if all docs are deleted in a posting list

[BubbleCal]

fix #3012

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.00%. Comparing base (d79e870) to head (4e8227f).
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3163      +/-   ##
==========================================
+ Coverage   77.95%   78.00%   +0.05%     
==========================================
  Files         242      243       +1     
  Lines       82436    82834     +398     
  Branches    82436    82834     +398     
==========================================
+ Hits        64262    64614     +352     
- Misses      14960    15006      +46     
  Partials     3214     3214              

Flag	Coverage Δ
unittests	78.00% <100.00%> (+0.05%)	⬆️

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