[macOS] ColorPicker doesn't work when the Color window is in the primary monitor and pick a color from the secondary monitor using the ColorPicker.

Steps to Repro:
1. Open the attached or create a new project.
2. Create a new material.
3. Open Color window by clicking Albedo color(Consider Color window is placed on the 1st monitor).
4. Click on ColorPicker.
5. Move the pointer around on 2nd monitor and select color.

Actual Result:
ColorPicker doesn't pick any color.

Expected Result:
Correct color should be picked.

Environment:
Mac

Occurring with:
2018.3.0b2, 2017.2.0f3