ConcurrentMessageQueue should search treiber stack in isIdle

This fixes a test failure I was seeing in CtsOsTestCasesRavenwood:android.os.cts.MessageQueueTest#testIsIdle

Flag: build.RELEASE_PACKAGE_MESSAGEQUEUE_IMPLEMENTATION
Test: atest CtsOsTestCasesRavenwood:android.os.cts.MessageQueueTest
Bug: 336880969
Change-Id: I5de8f9923621f02f72f22cff0324b59765454653
1 file changed