Blender Git Loki

Fix T63675: Keying outside NLA strip not possible

Allow adding keys outside of the NLA strip, when Sync Length is
activated. Before this, an animator would have to exit tweak mode,
adjust the strip length, then enter tweak mode again.

Now the animator can freely insert and modify keys outside of the strip
bounds. They will never have to touch the strip bounds directly.

Reviewed By: sybren

Differential Revision: https://developer.blender.org/D7533