evas_object_image_file_set can receives null to unset
evas_object_image_file_set can receives null to unset

Passing null to the second parameter is the only way to unset
the file, so it should not have EINA_ARG_NONNULL to the file parameter

git-svn-id: 24a995eca3b83137dd7eab3408044d7832e202f7@54998 7cbeb6ba-43b4-40fd-8cce-4c39aea84d33

antognolli/Evas,antognolli/Evas,antognolli/Evas,antognolli/Evas