Snapserver responses to return at least one response

[jframe]

PR description

The snap server responses must return at least one response item if the data can be retrieved according to the spec https://github.com/ethereum/devp2p/blob/master/caps/snap.md. This applies to all the request types.

After making this change all the GetByteCodes hive tests are passing. Note still need to make a change to hive testsuite to enable snapserver before this will be seen.

Fixed Issue(s)

Part of #7197

Thanks for sending a pull request! Have you done the following?

• [ ] Checked out our contribution guidelines?
• [ ] Considered documentation and added the doc-change-required label to this PR if updates are required.
• [ ] Considered the changelog and included an update if required.
• [ ] For database changes (e.g. KeyValueSegmentIdentifier) considered compatibility and performed forwards and backwards compatibility tests

Locally, you can run these tests to catch failures early:

• [ ] unit tests: ./gradlew build
• [ ] acceptance tests: ./gradlew acceptanceTest
• [ ] integration tests: ./gradlew integrationTest
• [ ] reference tests: ./gradlew ethereum:referenceTests:referenceTests