fix shardtree initialization failure

[AloeareV]

No description provided.

[zancas]

The tests now pass!

[codecov-commenter]

Codecov Report

Patch coverage: 82.85% and project coverage change: +0.85% 🎉

Comparison is base (92667ac) 59.81% compared to head (845e5a3) 60.66%.
Report is 2 commits behind head on dev.

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Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #486      +/-   ##
==========================================
+ Coverage   59.81%   60.66%   +0.85%     
==========================================
  Files          33       33              
  Lines        5412     5420       +8     
==========================================
+ Hits         3237     3288      +51     
+ Misses       2175     2132      -43     

Files Changed	Coverage Δ
zingocli/tests/integration_tests.rs	72.50% <ø> (ø)
zingolib/src/wallet.rs	66.77% <0.00%> (+2.21%)	⬆️
zingolib/src/lightclient.rs	64.53% <66.66%> (+1.60%)	⬆️
zingo-testutils/src/lib.rs	88.94% <92.00%> (+4.86%)	⬆️

... and 2 files with indirect coverage changes

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