Steps to reproduce:

1. Open a new scene, and bake the lighting
2. Navigate to Lighting Settings > Baked Lightmaps, and open the resulting lightmap
3. Begin adjusting the exposure by dragging the scrubber (LMB over the exposure icon)
4. Notice that this way, you can go beyond the hard-coded limit (-10, 10)

Notes:

- Min and max values can also be overridden by typing in any value in the float field