Fix bug "spieFeed Missing Item Level Images #11"

https://github.com/goldsky/spiefeed/issues/11
Fix spiefeed "Call to a member function get_uri() on a non-object"

Bug report: https://github.com/simplepie/simplepie/issues/214
Fix source: https://github.com/simplepie/simplepie/issues/214#issuecomment-7814156
Added Dutch translation
Merge pull request #12 from vierkantemeter/master

Fixed #11 and Call to a member function get_uri() on a non-object error