#196 cannot copy/paste/delete on extended frame

[Mj Mendoza IV]

to replicate:

1. create 1 frame
2. draw
3. extend the frame 10 times
4. select frame 5
5. try to delete/copy/paste

it won't let you.

[Mj Mendoza IV]

Fixed in https://sourceforge.net/p/kage/code/815/