Pasting images from one project to another crashes the editor

[zachrispoli]

Reproduce:

1. Make a new project in a tab
2. Make another new project in another tab
3. Import an image (e.g. image.jpeg) into the first project, copy it
4. Paste that image into the second project in the other tab

The second project will try to find the image in the asset library, but that asset doesn't exist! (basically the editor tries to load image.jpeg, gets undefined or null, and tries to give that to paper.js - then the crash happens.)