some check about jsonRpc

[scf0220]

1:

pyquarkchain/quarkchain/cluster/master.py

Line 1163 in 7886723

check(

need check?
if one shard have not been created?

2:

pyquarkchain/quarkchain/cluster/jsonrpc.py

Line 568 in 7886723

self.master.env.quark_chain_config.CHAIN_SIZE

if one shard have not been created?
return shards which have be created?

[qizhou]

1, Even shard is not created, the mapping from branch to slave should be created and get account data should just return pre-genesis data

2, This is a bit tricky. I think we may just return the size of chains that are created.