Support non-playable non-directory item, which will be runned as script by xbmc

In recent xbmc versions, it popup when the listing dir return with failure, which is not same as before, so I checked the xbmc code, found it's possible return to xbmc item which is neither playable nor directory, xbmc will run it as script, it's very useful when we want implement click an item but just run some script/function rather than really play an item or listing dir.

so here's the PR to let swift2 support return this type of item to xbmc.