Core: display $Z as Artist - Title

This is more coherent with the rest of the worlds...

src/text/strings.c

@@ -795,17 +795,17 @@ char *str_format_meta( playlist_t *p_object, const char *string )
                     if( p_item )
                     {
                         char *psz_now_playing = input_item_GetNowPlaying( p_item );
-                        if ( psz_now_playing == NULL )
+                        if( EMPTY_STR( psz_now_playing ) )
                         {
                             char *psz_temp = input_item_GetTitleFbName( p_item );
                             char *psz_artist = input_item_GetArtist( p_item );
-                            if( !EMPTY_STR( psz_temp ) )
+                            if( !EMPTY_STR( psz_artist ) )
                             {
-                                INSERT_STRING( psz_temp );
-                                if ( !EMPTY_STR( psz_artist ) )
+                                INSERT_STRING( psz_artist );
+                                if ( !EMPTY_STR( psz_temp ) )
                                     INSERT_STRING_NO_FREE( " - " );
                             }
-                            INSERT_STRING( psz_artist );
+                            INSERT_STRING( psz_temp );
                         }
                         else
                             INSERT_STRING( psz_now_playing );