Currently, invalid PeerConnection object is returned. With this change, null is returned instead. This can be more easily handled in the application layer. Bug: webrtc:9440 Change-Id: I44dfee81a681f033b8d336c999d43ff1c69fb015 Reviewed-on: https://webrtc-review.googlesource.com/98480 Reviewed-by: Magnus Jedvert <magjed@webrtc.org> Commit-Queue: Sami Kalliomäki <sakal@webrtc.org> Cr-Commit-Position: refs/heads/master@{#24637}