Changing Montage Section to a time beyond the current length breaks animation

User is able to set the Section Time to a value that's beyond the current length of the montage. This breaks the animation and the user can see issues in the UI as well (such as the timeline marker actually moving off the bar).

1. Open QAGame in editor.
2. Create a new animation montage based on UE4_Mannequin_Skeleton.
3. Open the montage.
4. Add an animation to the level. Note the length of the animation.
5. Right-click in the Montage timeline and select New Montage Section. Give it a name.
6. Right-click the section and set the Section Time to something beyond the length of the animation.

RESULT

The new time location is accepted. When the animation plays, it's stop animation at final frame but the timeline will continue.