The sink is only added once, but before this fix, the value was
updated to the same value, causing a tsan failure. This CL adds
a check so we don't update the value if it's set.
Bug: webrtc:10909
Change-Id: I46c8f7044f1441c0155b18881d1b8e0aeb7568c6
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/150783
Reviewed-by: Åsa Persson <asapersson@webrtc.org>
Commit-Queue: Sebastian Jansson <srte@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#28999}
7fa42778b4