input/meta.c: Make sure we don't return VLC_SUCCESS in __input_FindArtInCache when no album art was found.

(Oh, I am well aware that this is often not correctly set, but then again,
 why the heck would someone wants to parse the SDP origin in real life?)

              * Use filename sanitization at the lower level

- Some cleanup

Finally rid of the strcasestr warning

There is something seriously messed up in these files though
(like the declaration in xtag.h do not match the definition in xtag.c!)