tendermint-rs: Disallow a block height of 0

[tarcieri]

Tendermint itself says: "Height must be greater than 0" (code -32603)

[liamsi]

While (in Tendermint) the block height indeed needs to be greater than 0 it seems like the height fields (in proposal etc) are only checked against >= 0:
https://github.com/tendermint/tendermint/blob/4253e67c07c69be6d7f7263ab03944ce30a9fc90/types/proposal.go#L51

I would want to double check if this isn’t intentional in Tendermint before mergin this.

[tarcieri]

@liamsi sounds good, will hold off.

I know there are a few cases where the block height is represented as 0 (e.g. in priv_validator_state.json) as a placeholder for an uninitialized state.

My personal preference in Rust would be to disallow 0 as a valid block height and use Option<block::Height> to represent potentially uninitialized cases.

[liamsi]

My personal preference in Rust would be to disallow 0 as a valid block height and use Optionblock::Height to represent potentially uninitialized cases.

That sounds good to me 👍 Unfortunately, golang doesn't provide us with the same expressiveness as Rust.