playlist demux: do not set empty art URL

modules/demux/playlist/podcast.c

@@ -210,7 +210,7 @@ static int Demux( demux_t *p_demux )
                 }
                 else
                 {
-                    if( !strcmp( psz_elname, "url" ) )
+                    if( !strcmp( psz_elname, "url" ) && *node )
                     {
                         free( psz_art_url );
                         psz_art_url = strdup( node );

modules/demux/playlist/xspf.c

@@ -547,7 +547,7 @@ static bool set_item_info SIMPLE_INTERFACE
         input_item_SetDescription(p_input, psz_value);
     else if (!strcmp(psz_name, "info"))
         input_item_SetURL(p_input, psz_value);
-    else if (!strcmp(psz_name, "image"))
+    else if (!strcmp(psz_name, "image") && *psz_value)
         input_item_SetArtURL(p_input, psz_value);
     return true;
 }