[Lens] Heatmap with numeric color stops fail to load in dashboard

[dej611]

Describe the bug:

Dashboard cannot load a Heatmap with absolute number value defined palette color stops.

Steps to reproduce:

1. Create a dashboard
2. Create a Heatmap visualization via Lens
3. Open the Heatmap metric dimension panel and click on the palette to customize it
4. Just click the Number button
5. Save and return
6. 💥

Expected behavior:

The heatmap should load correctly as with percentage version.

Screenshots (if relevant):

Errors in browser console (if relevant):

Detected an unhandled Promise rejection.
TypeError: Cannot read property 'min' of undefined
utils.ts:97 Uncaught (in promise) TypeError: Cannot read property 'min' of undefined
    at getDataMinMax (utils.ts:97)
    at getOverallMinMax (utils.ts:85)
    at getPaletteStops (utils.ts:118)
    at applyPaletteParams (utils.ts:32)
    at getSafePaletteParams (utils.ts:19)
    at Object.getConfiguration (visualization.tsx:157)
    at state_helpers.ts:137
    at Array.reduce (<anonymous>)
    at validateDatasourceAndVisualization (state_helpers.ts:136)
    at persistedStateToExpression (state_helpers.ts:91)

Any additional context:

It seems that on embeddable bootstrap the frame.activeData gets accessed while it holds no data yet, leading to the code to throw an error.

[elasticmachine]

Pinging @elastic/kibana-vis-editors (Team:VisEditors)