fix:lib/trie: fix trie.NextKey case

[noot]

Changes

• the spec team pointed out an issue with the new trie.NextKey function, this fixes that case

Tests

go test ./lib/trie

Checklist

• I have read CODE_OF_CONDUCT and CONTRIBUTING
• I have provided as much information as possible and necessary
• I have reviewed my own pull request before requesting a review
• All integration tests and required coverage checks are passing

Issues

• related to fix and enable trie.NextKey #1439

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (development@7673637). Click here to learn what that means.
The diff coverage is n/a.

@@              Coverage Diff               @@
##             development    #1463   +/-   ##
==============================================
  Coverage               ?   57.74%           
==============================================
  Files                  ?      152           
  Lines                  ?    15315           
  Branches               ?        0           
==============================================
  Hits                   ?     8843           
  Misses                 ?     4927           
  Partials               ?     1545           

Flag	Coverage Δ
unittests	57.74% <0.00%> (?)

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