To reproduce:
1. Create a new project.
2. Create Empty game object in hierarchy.
3. Add Cloth component to it.
4. Set Cloth's "Stretching Stiffness" to 0. Error pops up: value must be greater than 0 UnityEditor.DockArea:OnGUI()
5. Set Cloth's "Collision Mass Scale" to -1. Error pops up: value must be greater than or equal to 0 UnityEditor.DockArea:OnGUI()
6. Set Cloth's "Solver Frequency" to 0. Error pops up: value must be greater than or equal to 1 UnityEditor.DockArea:OnGUI()
7. Set Cloth's "Sleep Threshold" to -1. Error pops up: value must be greater than or equal to 0 UnityEditor.DockArea:OnGUI()

Expected result: No errors. Value becomes the closest viable value. (just like in every other component)

Reproducible: 5.4.5p1, 5.5.3f1, 5.6.0f3, 2017.1.0b1