histograms: Fix parsing float histograms without zero bucket

If a float histogram has a zero bucket with a threshold of zero _and_
an empty zero bucket, it wasn't identified as a native histogram
because the `isNativeHistogram` helper function only looked at integer
buckets.

Signed-off-by: beorn7 <beorn@grafana.com>

model/textparse/protobufparse.go

@@ -105,7 +105,7 @@ func (p *ProtobufParser) Series() ([]byte, *int64, float64) {
 			v = float64(s.GetSampleCount())
 		case -1:
 			v = s.GetSampleSum()
-			// Need to detect a summaries without quantile here.
+			// Need to detect summaries without quantile here.
 			if len(s.GetQuantile()) == 0 {
 				p.fieldsDone = true
 			}
@@ -564,8 +564,10 @@ func formatOpenMetricsFloat(f float64) string {
 // deciding if a histogram should be ingested as a conventional one or a native
 // one.
 func isNativeHistogram(h *dto.Histogram) bool {
-	return len(h.GetNegativeDelta()) > 0 ||
-		len(h.GetPositiveDelta()) > 0 ||
+	return h.GetZeroThreshold() > 0 ||
 		h.GetZeroCount() > 0 ||
-		h.GetZeroThreshold() > 0
+		len(h.GetNegativeDelta()) > 0 ||
+		len(h.GetPositiveDelta()) > 0 ||
+		len(h.GetNegativeCount()) > 0 ||
+		len(h.GetPositiveCount()) > 0
 }