Fail early on `StateDB` functions

[fedekunze]

Most of the functions from statedb.go perform a no-operation (no-op) when an error is encountered. The problem is, that these functions don't have any context of whether previous calls failed or not. For example, both GetCodeHash and GetNonce require the account to exist before returning the value.

Solution:

Introduce a stateErr error field on the Keeper and return early on every StateDB method if there is a previous error registered.

[yihuang]

Just panic should be good? since the cosmos-sdk call will recover the panic.

[fedekunze]

no, it shouldn't panic, just fail early

[yihuang]

https://github.com/ethereum/go-ethereum/blob/master/core/state/statedb.go#L299
In go-ethereum, the query apis just returns a empty value when things not found.

[tomtau]

being worked on by @davcrypto

[davcrypto]

@tomtau yup, please help to assign to me first