Return null if media notification controller Future is not done

When the media notification controller is requested for a session
with `getConnectedControllerForSession` and the `Future` is not null
but not yet completed, the `Future` was returned either way. This was
reported as creating a race condition between the notification
being requested for update the very first time, and the media
notification controller having completed connecting to the session.

Returning null from `getConnectedControllerForSession` when the
`Future` is available but not yet done fixes the problem. This is
safe because for the case when a notification update is dropped,
the media notification controller will trigger the update as soon
as the connection completes.

Issue: #917
#minor-release
PiperOrigin-RevId: 595699929
(cherry picked from commit 5c50b27)

Author: marcbaechinger

RELEASENOTES.md

@@ -66,6 +66,9 @@
     *   Fix a bug where setting a negative time for a disabled `setWhen` timer
         of the notification caused a crash on some devices
         ([#903](https://github.com/androidx/media/issues/903)).
+    *   Fix `IllegalStateException` when the media notification controller
+        hasn't completed connecting when the first notification update is
+        requested ([#917](https://github.com/androidx/media/issues/917)).
 *   UI:
     *   Fix issue where forward and rewind buttons are not visible when used
         with Material Design in a BottomSheetDialogFragment

libraries/session/src/main/java/androidx/media3/session/MediaNotificationManager.java

@@ -262,7 +262,7 @@ private boolean shouldShowNotification(MediaSession session) {
   @Nullable
   private MediaController getConnectedControllerForSession(MediaSession session) {
     ListenableFuture<MediaController> controller = controllerMap.get(session);
-    if (controller == null) {
+    if (controller == null || !controller.isDone()) {
       return null;
     }
     try {