Avoid touching channel after OnSctpDataChannelClosed

Bug: chromium:1454086
Change-Id: I39573b706c4031d091c45a182b13cb3b2dba6233
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/309920
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#40332}

pc/data_channel_controller.cc

@@ -70,15 +70,19 @@ void DataChannelController::OnChannelStateChanged(
     SctpDataChannel* channel,
     DataChannelInterface::DataState state) {
   RTC_DCHECK_RUN_ON(network_thread());
+
+  // Stash away the internal id here in case `OnSctpDataChannelClosed` ends up
+  // releasing the last reference to the channel.
+  const int channel_id = channel->internal_id();
+
   if (state == DataChannelInterface::DataState::kClosed)
     OnSctpDataChannelClosed(channel);
 
   DataChannelUsage channel_usage = sctp_data_channels_n_.empty()
                                        ? DataChannelUsage::kHaveBeenUsed
                                        : DataChannelUsage::kInUse;
   signaling_thread()->PostTask(SafeTask(
-      signaling_safety_.flag(), [this, channel_id = channel->internal_id(),
-                                 state = state, channel_usage] {
+      signaling_safety_.flag(), [this, channel_id, state, channel_usage] {
         RTC_DCHECK_RUN_ON(signaling_thread());
         channel_usage_ = channel_usage;
         pc_->OnSctpDataChannelStateChanged(channel_id, state);