[Clone Stamp tool] Crash trying to reference garbage collected variable

[pedropaulosuzuki]

Description
I was just messing around with the Clone Stamp tool selected and saw Pinta crashing due to a garbage collected variable trying to be accessed.

To Reproduce
Not sure the optimal steps to reproduce, but I was able to do it twice by doing the following:

1. Open Pinta
2. Select the clone tool
3. Left click drag and right click drag on canvas
4. Wait a few minutes (for the reference to be garbage collected)
5. Left click drag and right click drag again

Additional Info

Unhandled exception. System.Exception: Could not toggle reference to strong. It got garbage collected.
   at GObject.Internal.ToggleRef.ToggleReference(Boolean isLastRef)
   at GObject.Internal.InstanceCache.ToggleNotify(IntPtr data, IntPtr object, Int32 isLastRef)

Version
Latest git

[cameronwhite]

I haven't been able to reproduce it yet, but wasn't sure about the right clicking mentioned in the instructions (the clone stamp tool just supports left clicking or ctrl+clicking)

Does the --debug command line flag make it easier for you to track down what triggers it? (that mode runs the GC much more frequently)