Bug#941633: synfigstudio crashes on almost every operation

[VA]

retitle 941633 synfigstudio crashes on almost every operation
severity 941633 serious
thanks

In fact, it's much more general than just when importing an image, it 
crashes for almost everything.

Here are a few example scenarios where synfigstudio crashes:

- start synfigstudio
- draw a rectangle
- press ctrl-z (undo)
-> synfigstudio segfaults

or

- start synfigstudio
- draw 2 rectangles
- select both rectangles
- choose "group layer"
-> synfigstudio segfaults

etc.

Sometimes it doesn't segfault but will fail to do something basic:

- start synfigstudio
- draw a rectangle
- delete the rectangle layer
-> synfigstudio doesn't do it and pop an error dialog mentioning 
"std::exception"

Same when trying to move layers, etc.

In this current state, synfigstudio is unusable.