Guard MediaDeviceManager.Entry against successive stop calls

This is a cherrypick of commit 543dd362fe.

It's non obvious from the code that an entry will be stopped
only once. The start() protection is added for simmetry.

Bug: 232812007
Test: Manual behavioral test.
Test: atest MediaDeviceManagerTest MediaDataCombineLatestTest
Change-Id: Icb4573d30790b4055b67eff57c495ceb6c3ae61b
Merged-In: Icb4573d30790b4055b67eff57c495ceb6c3ae61b

packages/SystemUI/src/com/android/systemui/media/MediaDeviceManager.kt

@@ -188,6 +188,7 @@ class MediaDeviceManager @Inject constructor(
 
         @AnyThread
         fun start() = bgExecutor.execute {
+            if (!started) {
                 localMediaManager.registerCallback(this)
                 localMediaManager.startScan()
                 muteAwaitConnectionManager?.startListening()
@@ -197,9 +198,11 @@ class MediaDeviceManager @Inject constructor(
                 started = true
                 configurationController.addCallback(configListener)
             }
+        }
 
         @AnyThread
         fun stop() = bgExecutor.execute {
+            if (started) {
                 started = false
                 controller?.unregisterCallback(this)
                 localMediaManager.stopScan()
@@ -207,6 +210,7 @@ class MediaDeviceManager @Inject constructor(
                 muteAwaitConnectionManager?.stopListening()
                 configurationController.removeCallback(configListener)
             }
+        }
 
         fun dump(pw: PrintWriter) {
             val routingSession = controller?.let {