Since the lifetime of an SctpDataChannel is not strictly controlled
by its controller, the controller might go away before the channel
does. This CL guards against this.
Bug: webrtc:13931
Change-Id: I07046fe896d1a66bf89287429beb0587382a13a9
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/261940
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Florent Castelli <orphis@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#36852}
