evas: fix _evas_jpeg_membuf_src_skip bug

evas: fix _evas_jpeg_membuf_src_skip bug

If file was corrupted , the size value of app frame is bigger than real file
size.

For example, if somebody change file using editor, the file start with (FF
D8 FF E0 FF DB ..).

But real file size can be small than (FF DB).

In that case, _evas_jpeg_membuf_src_skip set src->pub.bytes_in_buffer to
negative value, it make crash later.

Signed-off-by: Jiyoun Park <jy0703.park@samsung.com>
git-svn-id: svn+ssh://svn.enlightenment.org/var/svn/e/trunk/evas@61222 7cbeb6ba-43b4-40fd-8cce-4c39aea84d33