How to reproduce:
1. Open Unity
2. Create a new project
3. Dock Inspector, Lighting and Lighting Explorer windows in a single horizontally resizable area
4. Open Inspector tab
5. Resize Editor area to lowest width available
6. Switch to Lighting and Light Explorer windows

Expected result: Unity won't let resizable area get smaller than maximum 'minimal width' value of all docked windows(in the same resizable area)
Actual result: Unity allows resizing to minimal inspector width that is smaller than Lighting and Light Explorer windows resulting in layout problems

Reproducible with - 2017.3.0a5, 2017.3.0p3, 2018.1.0b4
Could not test with - 5.6.5p1, 2017.1.3f1, 2017.2.1p2, 2017.3.0a4(Current layout method was not implemented yet)