Fix genesis block sync

[shunsukew]

This PR fixes genesis block not accessible issue (#78) which blockchains started even before EthereumRuntimeRPCApi runtime API version 4 (current version) still have.

Because some blockchains have runtime API version lower than 4 at genesis block, has_api conditional becomes false for those blockchains. (fn has_api returns false if version mismatch). That means, ethereum genesis block cannot be properly mapped. (For example, our chains have runtime API version 1 at genesis block). Regardless of the runtime version blockchains have at genesis block, it should be properly synced.

[shunsukew]

@sorpaas @tgmichel @koushiro
Changes should be small, could you kindly give me feedback about this?
Thank you in advance

[sorpaas]

Sorry for the delay, but I think this is not really right. As I recall there were indeed some changes to current_block in version 2.

Please add an extra branch:

• If API version is equal or smaller than 2, call current_block_before_version_2.
• Otherwise, call current_block.

[shunsukew]

@sorpaas
Thank you so much for reviewing! (For some reason, I didn't notice notification and saw the review now.)

I see, I didn't know the background about changes to current_block. please let me do it.

[shunsukew]

@sorpaas
In other places, current_block_before_version_2 is called when API version is smaller than 2. If it is equal to 2, current_block is called.
For example, here
https://github.com/paritytech/frontier/blob/3173b07a166a8930b4cb1e69d34f2ba52ef4e9f3/client/rpc/src/eth/execute.rs#L126

Judging from EthereumRuntimeRPCApi definition, I think current_block should be called if version is 2 .
https://github.com/paritytech/frontier/blob/3173b07a166a8930b4cb1e69d34f2ba52ef4e9f3/primitives/rpc/src/lib.rs#L126

[sorpaas]

Hmm looks like Github bugged out and it refused to run CI for the last commit. I also couldn't find any button to retry the deployment. Would you mind to push a new empty commit?

[shunsukew]

Sure, pushed now! and it seems CI got triggered properly this time