When adding or editing a detail mesh in the terrain tools, the fields allow you to enter a minimum value larger than the maximum value.

1. Create a new unity project.
2. Create a new terrain in scene. (Right-click in Hierarchy -> 3D Object -> Terrain)
3. Select the terrain in Hierarchy to view in inspector.
4. In inspector, click the 'Paint Details' tab.
5. Click the 'Edit Details' button and then 'Add Detail Mesh'.
6. Enter any Min field to be larger than the Max field.

Expected Outcome: The min width is not allowed to be larger than the max width. Either the max width should increase to match. This is how it works with the 'Add Grass Texture' window, which is almost visually identical to 'Add Detail Mesh'.

Actual Outcome: Nothing happens. The min width/height field is accepted with no complaint.

Reproducible in 2019.3.0f4, 2017.4.32f1. Not a regression.