Camera Shake Oscillation Duration no longer accepts -1 as indefinite

The Camera Shake Class no longer allows for indefinite shaking via setting a negative value in the Oscillation duration, per the tooltip instructions. This happens when using either the Play World Camera Shake or the Play Camera Shake nodes.

This is a regression from 4.7.6.

Also tested in Preview 1 4.9.0-2633546, and Main Promotable - 4.10.0-2633501

1. Open QAGame Editor
2. Create a Blueprint based on Camera Shake Class, named BP_Shake
3. In BP_Shake, set Oscillation Duration to -1
4. In BP_Shake, set Loc Oscillation >> X >> Amplitude to 10 and Frequency to 20
5. Add a Camera into the Level
6. Create a BP from Placed Camera
7. In the CameraActor_Blueprint, set Auto Activate for Player to Player0
8. In the Level BP, Get Player Controller
9. From Get Player COntroller, Get Player Camera Manager
10. From Player Camera Manager, Play Camera Shake
11. Assign the BP_Shake to Shake Class of Play Camera Shake Node
12. Call a Key Press to Play Camera Shake
13. Compile and Save

RESULTS: The Camera Shake only fires once on key press, does not play indefinitely

EXPECTED: The Camera Shake should fire and play indefinitely.