fix(mqe): only parse none empty functions

pkg/tsdb/mqe/model_parser.go

@@ -49,8 +49,10 @@ func (qp *QueryParser) Parse(model *simplejson.Json, dsInfo *models.DataSource,
 			return nil, err
 		}
 
+		if f.Func != "" {
 			functions = append(functions, f)
 		}
+	}
 
 	query.FunctionList = functions