Use TryGetReaderAtTablePosition

[JimBobSquarePants]

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Description

Fixes #333

[codecov]

Codecov Report

Merging #338 (960f46c) into main (548b017) will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##            main    #338   +/-   ##
=====================================
  Coverage     83%     83%           
=====================================
  Files        227     227           
  Lines      12859   12859           
  Branches    1838    1839    +1     
=====================================
  Hits       10772   10772           
  Misses      1652    1652           
  Partials     435     435           

Flag	Coverage Δ
unittests	83% <100%> (ø)

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Impacted Files	Coverage Δ
src/SixLabors.Fonts/Tables/TableLoader.cs	91% <ø> (ø)
src/SixLabors.Fonts/FontReader.cs	97% <100%> (ø)
...abors.Fonts/Tables/General/VerticalMetricsTable.cs	83% <100%> (ø)

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