fix: add proof size check when the VRF proof is empty

[170210]

Description

This PR added an error handle in proof size check when the VRF proof is empty.

Previously, we allowed the proof hash to be 0 in Validateproof because there was no proof required when verifying Genesis block's information. However, since there is no Genesis block, the proof hash should not be zero in general verification.

I tested it with finschia-sdk, and there is no problem when this handling was added.

related #510

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 66.53%. Comparing base (fc54d22) to head (4a2f67b). Report is 3 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #765 +/- ## ========================================== - Coverage 66.58% 66.53% -0.05% ========================================== Files 285 285 Lines 37919 37917 -2 ========================================== - Hits 25248 25228 -20 - Misses 10871 10882 +11 - Partials 1800 1807 +7 ``` | [Files](https://app.codecov.io/gh/Finschia/ostracon/pull/765?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Finschia) | Coverage Δ | | |---|---|---| | [crypto/ed25519/migration.go](https://app.codecov.io/gh/Finschia/ostracon/pull/765?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Finschia#diff-Y3J5cHRvL2VkMjU1MTkvbWlncmF0aW9uLmdv) | `100.00% <100.00%> (+16.66%)` | :arrow_up: | ... and [17 files with indirect coverage changes](https://app.codecov.io/gh/Finschia/ostracon/pull/765/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Finschia)

[ulbqb]

https://github.com/Finschia/ostracon/blob/898b48c4c66a9e9a7e148f1b0e61669f3ba197f7/crypto/ed25519/migration.go#L41-L43

It looks like empty proofs are admitted intentionally. Would you research this?

[ulbqb]

Please add following contents to description:

• Related PRs
• Process where you decided to remove empty proof handling (What you tried)
• The reason where this handling was added

[ulbqb]

https://github.com/Finschia/ostracon/blob/ae67c39c8a79827fc0aeeddf86f64bdbf193cbf4/spec/core/data_structures.md?plain=1#L56 And update spec please.