elm_image: Fix preload for normal files
elm_image: Fix preload for normal files

grmbl, elm_image must explicitely start preload or the
image will stay blank if evas_object_show() is called before
elm_image_file_set().

FlorentRevest/Elementary,tasn/elementary,rvandegrift/elementary,tasn/elementary,FlorentRevest/Elementary,FlorentRevest/Elementary,rvandegrift/elementary,rvandegrift/elementary,tasn/elementary,FlorentRevest/Elementary,tasn/elementary,rvandegrift/elementary,tasn/elementary