GHSA-m6wq-66p2-c8pc: Babylon Nil BlockHash in BLS vote extensions triggers panics in consensus handlers

A vulnerability exists in Babylon’s BLS vote extension processing where a malicious active validator can submit a VoteExtension with the block_hash field omitted from the protobuf serialization. Because protobuf fields are optional, unmarshalling succeeds but leaves BlockHash as nil. Babylon then dereferences this nil pointer in consensus-critical code paths (notably VerifyVoteExtension, and also proposal-time vote verification), causing a runtime panic.