RPC endpoint chain_getEvents fails to get events by height

[ishantiw]

Expected behavior

chain_getEvents should return all the events emitted during block execution for a block height

Actual behavior

Returns error when getting by height even if the event was emitted

 "error": {
        "message": "Specified key 0900000076 does not exist",
        "code": -32600
    }

Steps to reproduce

• Run dpos-mainchain example app
• Call chain_getEvents RPC for a specific height

Which version(s) does this affect? (Environment, OS, etc...)

• 6.0.0-alpha.3