Undoing Selection Flip X / Y will delete the drawing

[Jose-Moreno]

Issue Summary

Testing the program I forgot to report this. Basically if you select an area and use the Selection Flip X / Y function and then undo that operation, the drawing will be deleted. You can redo the drawing being deleted to the flipped state though.

Current workaround is flipping the selection again in the same axis

Expected Results

Flipping Selection should be un-doable /re-doable

Steps to reproduce

1. Draw something
2. Press CTRL + A or Create a Box Selection over the strokes
3. Go to Edit > Selection > Flip x/y
4. Remove selection. You can keep it too, it doesn't matter.
5. Press CTRL + Z. Drawing disappears.

System Information

• Pencil2D Version:
  Version: 0.6.2
  commit: 6471882
  date: 2018-10-12_11:17:33
  Development build
  Operating System: Windows 7 SP 1 (6.1)
  CPU Architecture: x86_64

[MrStevns]

I'll check if I can reproduce this in the undo-redo rewrite branch.