RPC eth_getTransactionByBlockHashAndIndex does not work as expected when querying a non-existent transaction index

[banishee]

System info: [Include Ethermint commit, operating system name, and other relevant details]

Steps to reproduce:

1. Assuming the block in height n only has 1 transaction
2. A developer calls this api in such a parameter

params: [
   '0xe670ec64341771606e55d6b4ca35a1a6b75ee3d5145a99d05921026d1527331',
   '0xa' // 10
]

3. The result shows up an undefined error

{Code:-32000, Message:"{\"code\":1,\"log\":\"internal\",\"height\":1680,\"codespace\":\"undefined\"}

Expected behavior: [What you expected to happen]

• If a developer query an non-existent transaction, it's better for this api to return null rather than an error

Actual behavior: [What actually happened]

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

[github-actions]

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