segfault in block::signature_operations() when the validation.state is not present

[fpelliccioni]

This usually happens when we fetch a block from the database and the state metadata is not present.

See
https://github.com/k-nuth/domain/blob/97eb02e2457aa3bdffcfeb93b21f61258a60f36c/src/chain/block.cpp#L397

[fpelliccioni]

Fixed in https://github.com/k-nuth/kth/releases/tag/v0.4.1