nimiq-blockchain: Genesis batch set request

Nimiq is a Rust implementation of the Nimiq Proof-of-Stake protocol based on the Albatross consensus algorithm. Prior to version 1.5.0, a remote peer can crash any full node by sending a RequestBatchSet message containing the genesis block's hash. The handler calls get_epoch_chunks which iterates backwards through macro blocks using Policy::macro_block_before. When it reaches the genesis block number, macro_block_before panics with "No macro blocks before genesis block". This issue has been patched in version 1.5.0.