Animation curve's key time value can not be set to a negative number when typing the negative value using "Edit Key..."
Note: dragging the key to a negative value works just fine.

To reproduce:
1. Open the project attached by the user
2. Select "GameObject" from the Hierarchy
3. Press on the Curve that is attached to the game object to edit it
4. Press right mouse button on any of the keys
5. Select "Edit Key..."
6. Try to input a negative value for time property
7. Observe time value being set to 0

Expected: It is possible to set negative values for time using "Edit Key..." just like it is possible to drag the key to a negative value
Actual: Trying to set a negative time value for a key using "Edit Key..." sets the value to 0 instead

Reproduced on: 5.5.0b2, 5.4.0p3, 5.3.6p2, 5.2.5f1