Heatmap: Fix missing/wrong value in heatmap legend (#31430)

Co-authored-by: Torkel Ödegaard <torkel@grafana.com>

public/app/plugins/panel/heatmap/color_legend.ts

@@ -71,7 +71,7 @@ coreModule.directive('heatmapLegend', () => {
         clearLegend(elem);
         if (!_.isEmpty(ctrl.data) && !_.isEmpty(ctrl.data.cards)) {
           const cardStats = ctrl.data.cardStats;
-          const rangeFrom = _.isNil(panel.color.min) ? Math.min(cardStats.min, 0) : panel.color.min;
+          const rangeFrom = _.isNil(panel.color.min) ? Math.max(cardStats.min, 0) : panel.color.min;
           const rangeTo = _.isNil(panel.color.max) ? cardStats.max : panel.color.max;
           const maxValue = cardStats.max;
           const minValue = cardStats.min;

public/app/plugins/panel/heatmap/rendering.ts

@@ -501,7 +501,7 @@ export class HeatmapRenderer {
     const cardsData = this.data.cards;
     const cardStats = this.data.cardStats;
     const maxValueAuto = cardStats.max;
-    const minValueAuto = Math.min(cardStats.min, 0);
+    const minValueAuto = Math.max(cardStats.min, 0);
     const maxValue = _.isNil(this.panel.color.max) ? maxValueAuto : this.panel.color.max;
     const minValue = _.isNil(this.panel.color.min) ? minValueAuto : this.panel.color.min;
     const colorScheme: any = _.find(this.ctrl.colorSchemes, {