Fix the GUI_MSG_WINDOW_DEINIT message to include the next window id as param1

which is designed should be there, but missed in current code, I made it up.

and existed codes using GetParam1 on the message to get next window is include:
CGUIWindow::OnMessage which then call OnDeinitWindow(int nextWindowID) with it but seems current it is always 0, this commit fixed this.
CGUIWindowPictures::OnMessage according whether it is going to the slideshow window to decide whether unload imagelib.