Save whiteboard edits: bugs

[sander]

I found 2 bugs in the save whiteboard edits logic:

1) When you draw something in the whiteboard, then Undo everything again, and then close the whiteboard, you are still asked to save the changes while there was nothing changed.

2) When you changed something in the whiteboard and close the whiteboard, you can press "Yes". In the new dialog to enter the file name you can choose to Cancel. However, when you choose "Cancel", the whiteboard is still closed and you lose all your changes! This is a major usability bug!