Fixed "local variable 'file_type' referenced before assignment" if image type wasn't known.
No longer write image back to source image file if nothing has changed for better performance. The motivation here is that I've got 10000+ of images that I need to remove exif data from. Many of the images have already had exif removed previously. Thus writing unchanged data back to the source file was making batch processing take a lot longer than it needed to.
Coverage increased (+0.01%) to 94.896% when pulling 7b48d0f2de0961ca7fd36d452f490bc2a97a392a on jim-meyer:fixes into 3422fbe7a12c3ebcc90532d8e1f4e3be32ece80c on hMatoba:master.