Slider value goes out of range in the lightmap preview window.

Steps to repro:
1. Open the attached project.
2. Windows > Rendering > Lighting Settings.
3. In the lighting window open Baked Lightmap tab.
4. Double-click on the first baked lightmap in the list.

Actual Result:
Slider value goes out of range.

Expected result:
Slider value changes in the range.

Reproducible in:
2019.1.0a13, 2018.3.0f2(49866f0a5d12), 2018.3.0a8.

Note: Slider is introduced in Lightmap Preview Window from 2018.3.0a8.

Environment:
Windows & Mac