json-rpc test fail on pruned node

[yihuang]

System info: ethermint main

Steps to reproduce:

The issue is like this:

• After feat: Add GetParamSetIfExists to prevent panic on breaking param changes cosmos/cosmos-sdk#12615, the EvmKeeper.GetParams don't panic on pruned state anymore.
• JSON-RPC relies on that error return to know the state is pruned, so it'll fallback to parse the base-fee from block events.

Solution:

• JSON-RPC search block events as long as returned baseFee is nil, no matter what the error is.
• Somehow detect the pruned state in keeper and return an error instead.

Expected behavior: [What you expected to happen]

Actual behavior: [What actually happened]

Additional info: [Include gist of relevant config, logs, etc.]