Fix for no-return-in-nonvoid-function from rpm lint

Hi, I get this error from the rpm lint when trying to build Kodi for openSUSE. More over, in case of 'Release' build the assert in the 'default' case is being ignored.

I've created the following pull request https://github.com/xbmc/libdvdnav/pull/2 and was suggested to push it here, but I can't fork the repo and create a pull request.

Thanks, Sagi.