Resetting a custom brush resets the falloff curve to nothing

Problem: if you reset a custom brush, the falloff will reset to a curve with no points, resulting in a non-functioning brush until the falloff is set manually.

Repro steps:
1. Create a terrain
2. Select the terrain
3. Select the paint tab
4. Select the last brush on the list
5. Click the gear icon in the upper right of the custom brush segment
6. Click "reset"
7. Notice that the falloff no longer has a curve.

Expected result: the falloff curve should be reset to default, a linear line from 0,0 to 1,1
Actual result: the falloff curve is erased

License type: Pro