address comments

Signed-off-by: Ben Ye <yb532204897@gmail.com>

Author: yeya24

pkg/api/query/v1.go

@@ -427,7 +427,6 @@ func (qapi *QueryAPI) labelValues(r *http.Request) (interface{}, []error, *api.A
 	if err != nil {
 		return nil, nil, &api.ApiError{Typ: api.ErrorBadData, Err: err}
 	}
-	// Prometheus doesn't check this, do we need to?
 	if end.Before(start) {
 		err := errors.New("end timestamp must not be before start time")
 		return nil, nil, &api.ApiError{Typ: api.ErrorBadData, Err: err}
@@ -481,6 +480,10 @@ func (qapi *QueryAPI) series(r *http.Request) (interface{}, []error, *api.ApiErr
 	if err != nil {
 		return nil, nil, &api.ApiError{Typ: api.ErrorBadData, Err: err}
 	}
+	if end.Before(start) {
+		err := errors.New("end timestamp must not be before start time")
+		return nil, nil, &api.ApiError{Typ: api.ErrorBadData, Err: err}
+	}
 
 	var matcherSets [][]*labels.Matcher
 	for _, s := range r.Form["match[]"] {