Heatmap: Fix color rendering for value ranges < 1 (#68156)

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

@@ -967,7 +967,7 @@ export const boundedMinMax = (
 };
 
 export const valuesToFills = (values: number[], palette: string[], minValue: number, maxValue: number) => {
-  let range = Math.max(maxValue - minValue, 1);
+  let range = maxValue - minValue || 1;
 
   let paletteSize = palette.length;