soroban-rpc: getHealth should not fail if called with an empty parameter array.

[paulbellamy]

Currently if you call getHealth with params: [], it throws. For example:

curl -v \
  -X POST \
  --header "content-type: application/json" \
  http://localhost:8000/soroban/rpc \
  --data-binary '{"jsonrpc":"2.0", "id":2, "method":"getHealth", "params": []}'

[sreuland]

yes, noticed similar error response on other rpc methods that don't require a params. The error message varies a bit, but appears to be same root issue of empty params: [] in the request.