Bug 17879: Use image filename if no image name is entered

Bug 17879: Use image filename if no image name is entered

This patch changes the code to use the filename of the uploaded image if
no specific image name is entered.

To test:
1) Go to Tools -> Patron card creator -> Manage images
2) Upload an image and leave the image name field empty
3) Notice this works and 'Name' is left empty.
4) Apply patch and refresh page
5) Upload an image and leave the image name field empty
6) Notice the image name is given the filename so that 'Name' is no
longer empty.

Sponsored-by: Catalyst IT
Signed-off-by: Claire Gravely <claire_gravely@hotmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>