Blender Git Loki

Bugfix #24535: File saved with NLA Strip in Tweakmode crashes on reload

Now the active strip doesn't just get cleared on fileload, but is relinked properly.

I had originally intended that files shouldn't be able to be saved with NLA data still in Tweakmode, but this turns out to be a bit more troublesome to get working as that would make undo keep popping out of this mode too.

Also reverting 32743 (bugfix for 24418), which was a hack around this.