Evas image: reset error after setting a proxy.

Evas image: reset error after setting a proxy.

evas_object_image_file_set tries to load the file even if the file is NULL,
this in turn makes proxies always report about an error, although there
isn't really one.
I'm not sure whether evas_object_image_file_set should behave the way it
does, but I'm sure the proxy needs to reset the error anyway (because of
potential previous errors).

git-svn-id: svn+ssh://svn.enlightenment.org/var/svn/e/trunk/evas@74073 7cbeb6ba-43b4-40fd-8cce-4c39aea84d33