fix delta position in merge and index sorting

[PSeitz]

fixes #1125

[codecov]

Codecov Report

Merging #1132 (96a2239) into main (85d23e8) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1132      +/-   ##
==========================================
+ Coverage   89.47%   89.51%   +0.04%     
==========================================
  Files         203      203              
  Lines       20206    20256      +50     
==========================================
+ Hits        18079    18133      +54     
+ Misses       2127     2123       -4     

Impacted Files	Coverage Δ
src/indexer/merger.rs	89.56% <100.00%> (+<0.01%)	⬆️
src/indexer/merger_sorted_index_test.rs	100.00% <100.00%> (ø)
src/indexer/segment_updater.rs	88.73% <0.00%> (+1.07%)	⬆️

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