`zcash_client_sqlite` Fix error related to commitment tree frontier insertions.

[nuttycom]

Fixes #1398.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 60.00000% with 34 lines in your changes missing coverage. Please review.

Project coverage is 62.99%. Comparing base (976a4d2) to head (3e090dc). Report is 10 commits behind head on main.

Files	Patch %	Lines
zcash_client_sqlite/src/testing.rs	65.27%	25 Missing :warning:
...cash_client_backend/src/serialization/shardtree.rs	0.00%	4 Missing :warning:
zcash_client_sqlite/src/wallet/commitment_tree.rs	33.33%	2 Missing :warning:
zcash_client_sqlite/src/lib.rs	50.00%	1 Missing :warning:
zcash_client_sqlite/src/wallet.rs	50.00%	1 Missing :warning:
...te/src/wallet/init/migrations/shardtree_support.rs	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1396 +/- ## ========================================== - Coverage 63.13% 62.99% -0.14% ========================================== Files 126 126 Lines 14720 14762 +42 ========================================== + Hits 9293 9299 +6 - Misses 5427 5463 +36 ```

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[nuttycom]

force-pushed to address comments from code review.

[nuttycom]

force-pushed to address comments from review.