Pellicola: Handling photos without EXIF metadata

This one is straight from the Why haven't I thought about it before? department. In all this time, it has never occurred to me what would happen if I add a photo without EXIF data to Pellicola. Until, of course, I actually tried it. I was dismayed to discover that it breaks Pellicola big time. So I've come up with a fix that hopefully solves the problem.