promql: simplify rangeEval a bit more

We can't have both a float and a histogram at the same timestep.

Signed-off-by: Bryan Boreham <bjboreham@gmail.com>

promql/engine.go

@@ -1187,25 +1187,22 @@ func (ev *evaluator) rangeEval(prepSeries func(labels.Labels, *EvalSeriesHelper)
 				bufHelpers[i] = bufHelpers[i][:0]
 			}
 
-			add := func(si int, s Sample) {
-				vectors[i] = append(vectors[i], s)
-				if prepSeries != nil {
-					bufHelpers[i] = append(bufHelpers[i], seriesHelpers[i][si])
-				}
-				ev.currentSamples++
-			}
-
 			for si, series := range matrixes[i] {
 				if len(series.Floats) > 0 && series.Floats[0].T == ts {
-					add(si, Sample{Metric: series.Metric, F: series.Floats[0].F, T: ts})
+					vectors[i] = append(vectors[i], Sample{Metric: series.Metric, F: series.Floats[0].F, T: ts})
 					// Move input vectors forward so we don't have to re-scan the same
 					// past points at the next step.
 					matrixes[i][si].Floats = series.Floats[1:]
-				}
-				if len(series.Histograms) > 0 && series.Histograms[0].T == ts {
-					add(si, Sample{Metric: series.Metric, H: series.Histograms[0].H, T: ts})
+				} else if len(series.Histograms) > 0 && series.Histograms[0].T == ts {
+					vectors[i] = append(vectors[i], Sample{Metric: series.Metric, H: series.Histograms[0].H, T: ts})
 					matrixes[i][si].Histograms = series.Histograms[1:]
+				} else {
+					continue
+				}
+				if prepSeries != nil {
+					bufHelpers[i] = append(bufHelpers[i], seriesHelpers[i][si])
 				}
+				ev.currentSamples++
 				if ev.currentSamples > ev.maxSamples {
 					ev.error(ErrTooManySamples(env))
 				}