hwmap: set hwmap_class earlier in ngli_hwmap_map_frame()
hwmap: set hwmap_class earlier in ngli_hwmap_map_frame()

This will allow hwmap to call hwmap_class->uninit() next time
hwmap_reset() is called even if hwmap_class->init() failed.

Since hwmap_class is now set earlier, we need to ensure that both
hwmap_priv_data and hwmap_class are set before calling
hwmap_class->uninit().

gopro/gopro-lib-node.gl,gopro/gopro-lib-node.gl,gopro/gopro-lib-node.gl,gopro/gopro-lib-node.gl