Fix bounds of data read in VarList updates

[benjaminwinger]

When updating we are reading the size of the var list data column using the offset column's metadata.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (84f145c) 89.23% compared to head (beba021) 90.27%.
Report is 6 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2346      +/-   ##
==========================================
+ Coverage   89.23%   90.27%   +1.04%     
==========================================
  Files        1007     1011       +4     
  Lines       32224    32312      +88     
==========================================
+ Hits        28755    29170     +415     
+ Misses       3469     3142     -327     

Files	Coverage Δ
src/include/storage/store/column.h	84.21% <ø> (ø)
src/storage/store/column.cpp	87.77% <100.00%> (+0.23%)	⬆️
src/storage/store/var_list_column.cpp	99.02% <100.00%> (-0.02%)	⬇️

... and 47 files with indirect coverage changes

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