message: Fix event handling in json rpc server
  This commit removes the `unreachable` statement in the JSON-RPC server
  event handling `match` and replaces it with an error log.
  Additionally, fixed an faulty `if` condition introduced in previous
  commits.
diff: @@ -25,6 +25,7 @@ use std::{convert::Infallible, fmt::Debug, time::Instant};
  use datasize::DataSize;
  use futures::join;
  +use tracing::error;
  use casper_execution_engine::core::engine_state::{
  self, BalanceRequest, BalanceResult, GetBidsRequest, GetEraValidatorsError, QueryRequest,
  @@ -424,7 +425,7 @@ where
  main_responder,
  } if self.enable => main_responder.respond(peers).ignore(),
  Event::RpcRequest(RpcRequest::SpeculativeDeployExecute { .. })
  - if self.speculative_exec_enable =>
  + if !self.speculative_exec_enable =>
  {
  Effects::new()
  }
  @@ -441,7 +442,10 @@ where
  {
  Effects::new()
  }
  - _ => unreachable!(),
  + ev => {
  + error!("Unhandled event in JSON-RPC server: {}", ev);
  + Effects::new()
  + }
  }
  }
  }
  