Discard do not work as expected

Discarding a modified disk image (due dragging/importing a file) before dragging/importing further files, the disk image is not reseted. When application asks to discard a modified disk image, it should do that if the user decided to do so.

Rethink about this behavior! It isn't neseccary to ask the user to take the actual modification over. The user should be able to modify the disk image as long as the user stays on the same disk.