Problem: LastCommitID crashes when memiavl is not loaded first

[yihuang]

Solution:

• support the use case used by x/upgrade

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PR Checklist:

• Have you read the CONTRIBUTING.md?
• Does your PR follow the C4 patch requirements?
• Have you rebased your work on top of the latest master?
• Have you checked your code compiles? (make)
• Have you included tests for any non-trivial functionality?
• Have you checked your code passes the unit tests? (make test)
• Have you checked your code formatting is correct? (go fmt)
• Have you checked your basic code style is fine? (golangci-lint run)
• If you added any dependencies, have you checked they do not contain any known vulnerabilities? (go list -json -m all | nancy sleuth)
• If your changes affect the client infrastructure, have you run the integration test?
• If your changes affect public APIs, does your PR follow the C4 evolution of public contracts?
• If your code changes public APIs, have you incremented the crate version numbers and documented your changes in the CHANGELOG.md?
• If you are contributing for the first time, please read the agreement in CONTRIBUTING.md now and add a comment to this pull request stating that your PR is in accordance with the Developer's Certificate of Origin.

Thank you for your code, it's appreciated! :)

[codecov]

Codecov Report

Merging #1087 (04f8f06) into main (6ffbced) will decrease coverage by 0.05%.
The diff coverage is 34.14%.

@@            Coverage Diff             @@
##             main    #1087      +/-   ##
==========================================
- Coverage   46.20%   46.15%   -0.05%     
==========================================
  Files          80       80              
  Lines        7173     7197      +24     
==========================================
+ Hits         3314     3322       +8     
- Misses       3502     3518      +16     
  Partials      357      357              

Impacted Files	Coverage Δ
memiavl/db.go	55.24% <18.18%> (-1.81%)	⬇️
memiavl/multitree.go	72.53% <52.63%> (+0.59%)	⬆️