fix(client-core): Rejects command promises if client is not in ready …

…state. Prevents unresolved promises, memory leaks, and helps the object consuming the client maintain flow in case of errors.

src/modbus-client-core.js

@@ -181,6 +181,7 @@ module.exports = stampit()
         if (this.inState('closed')) {
           this.emit('error', 'connection closed')
         }
+        defer.reject({err: 'modbus client not in "ready" state'})
       }
     }