SurfaceFlinger: fix a potential race condition in stealReceiveChannel am:...

SurfaceFlinger: fix a potential race condition in stealReceiveChannel am: 899e8cd0 am: 2afe6245 am: b99ea55f

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/native/+/18764134



Change-Id: Ia67507fdaeeccedd08776f9edf2712b46789b27b
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>