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]

Codecov Report

All modified and coverable lines are covered by tests ✅

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

Additional details and impacted files

@@            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	Coverage Δ
crypto/ed25519/migration.go	100.00% <100.00%> (+16.66%)	⬆️

... and 17 files with indirect coverage changes

[ulbqb]

ostracon/crypto/ed25519/migration.go

Lines 41 to 43 in 898b48c

	// ValidateProof returns an error if the proof is not empty, but its
	// size != vrf.ProofSize.
	func ValidateProof(h []byte) error {

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]

ostracon/spec/core/data_structures.md

Line 56 in ae67c39

| Proof | slice of bytes (`[]byte`) | Proof is a vrf proof | Length of proof must be == 0 or == 80 (curve25519-voi) |

And update spec please.