Crash when pressing B button on playlists #16951 (#16971)

* Added check for null thumbnail path.  Applies to 16951

* Moved null check up the code to cover multiple accesses to the thumbnail path.

* Checked for null values before trying to get logo icons for playlists

* Rolled back the thumbnail_path_gfx changes and instead added
deinitialization of the icon thumbnails when a list was not a playlist.

menu/drivers/xmb.c

@@ -2958,9 +2958,14 @@ static void xmb_populate_entries(void *data,
 
    xmb_set_title(xmb);
 
-   if(xmb->is_playlist && settings->uints.menu_icon_thumbnails)
+   if(xmb->is_playlist)
    {
-      xmb_populate_dynamic_icons(xmb);
+      if(settings->uints.menu_icon_thumbnails)
+         xmb_populate_dynamic_icons(xmb);
+   } 
+   else if(xmb->thumbnails.pending_icons != XMB_PENDING_THUMBNAIL_NONE )
+   {
+      xmb_unload_icon_thumbnail_textures(xmb);
    }
 
    if (xmb->allow_dynamic_wallpaper)