Fix: Add missing continue statement in message validation

The message validation was missing a continue statement, causing
the handler to continue executing even after pushing an error response.
This led to undefined errors when trying to map over undefined values.

src/rpc.ts

@@ -712,6 +712,7 @@ export async function handleRpc(
           success: false,
           error: 'Missing or invalid message',
         });
+        continue;
       }
 
       if (!signature || typeof signature !== 'string') {