I was hitting strange bug when undoing just loaded nested edl was causing segfault.

After MUCH mucking around I think I discovered we were calling wrong function via pointer, I tested loading/undoing nested edl, normal edl, reference edl and group-loading 25+ pngs on separate tracks or as 25 pieces on same track. And undoing a lot!

But please test as hard as possible - threading is not my strong suit, actually it is not my suit at all!