pool: use safe type assertion

Author: elhimov

pool/connection_pool.go

@@ -1085,15 +1085,20 @@ func (p *ConnectionPool) getConnectionRole(conn *tarantool.Connection) (Role, er
 		return UnknownRole, ErrIncorrectResponse
 	}
 
-	instanceStatus, ok := data[0].(map[interface{}]interface{})["status"]
+	respFields, ok := data[0].(map[interface{}]interface{})
+	if !ok {
+		return UnknownRole, ErrIncorrectResponse
+	}
+
+	instanceStatus, ok := respFields["status"]
 	if !ok {
 		return UnknownRole, ErrIncorrectResponse
 	}
 	if instanceStatus != "running" {
 		return UnknownRole, ErrIncorrectStatus
 	}
 
-	replicaRole, ok := data[0].(map[interface{}]interface{})[roFieldName]
+	replicaRole, ok := respFields[roFieldName]
 	if !ok {
 		return UnknownRole, ErrIncorrectResponse
 	}