fix(querier): fixes panic when filtering agg metrics from nil resp (#17662)

pkg/querier/http.go

@@ -187,6 +187,11 @@ func (q *QuerierAPI) SeriesHandler(ctx context.Context, req *logproto.SeriesRequ
 	resLength := 0
 	if resp != nil {
 		resLength = len(resp.Series)
+
+		// filter the response to catch the empty matcher case
+		if !aggMetricsRequestedInAnyGroup && q.metricAggregationEnabled(ctx) {
+			resp = q.filterAggregatedMetricsFromSeriesResp(resp)
+		}
 	}
 
 	statResult := statsCtx.Result(time.Since(start), queueTime, resLength)
@@ -197,11 +202,6 @@ func (q *QuerierAPI) SeriesHandler(ctx context.Context, req *logproto.SeriesRequ
 	status, _ := serverutil.ClientHTTPStatusAndError(err)
 	logql.RecordSeriesQueryMetrics(ctx, utillog.Logger, req.Start, req.End, req.Groups, strconv.Itoa(status), req.GetShards(), statResult)
 
-	// filter the response to catch the empty matcher case
-	if !aggMetricsRequestedInAnyGroup && q.metricAggregationEnabled(ctx) {
-		return q.filterAggregatedMetricsFromSeriesResp(resp), statResult, err
-	}
-
 	return resp, statResult, err
 }