[Bug]: BlockID flag must be considered in Vote Extension Validation

[nivasan1]

What happened?

Problem

• the ValidateVoteExtensionFn in abci_utils.go attempts to check VoteExtensionSignature / VoteExtension even for votes that have the BlockID_Absent or BlockID_Nil, this should not be happening as the VoteExtension / Signature for these vote-types is nil, and will fail the check.

Consequences

• This leads to a liveness failure for chains using this check, as if every height, nodes that fail to include a pre-commit from any validator in their injected last-commit-info will cause the above check to fail, and the proposal to be rejected (in process or prepare (depends on implementation))

• p.s: from @SkipProtocol w/ ❤️

Cosmos SDK Version

v0.50.x

How to reproduce?

To Reproduce

• During any round of consensus, if any active validator goes down (or fails to participate in consensus / get their vote included in LastCommit) the block at the next height will fail to pass Process / Prepare proposal w/ the given error