Fix window ID retention. When the videostream restart after being deactivated...

Fix window ID retention. When the videostream restart after being deactivated (audio-only), we kept using an old window ID that was discard by the API client. When there is no video for a videostream, the videostream's window ID couldn't be set by the API client because no label was assigned. So on reset, we cannot use mNativeWindowId. Also, a window id can be NULL. So it must be use as-is even if it is null from participant device.