Restore player service start handling before player UI separation

This behavior was present before 0.24.0 and the player UI separation and
avoided crashes for which their exception contained
"Context.startForegroundService() did not then call Service.startForeground()".

Some player nullability checks have been also added, and the player service is
now stopped when it has been started from a media button and there is nothing
to play.

app/src/main/java/org/schabi/newpipe/player/PlayerService.java

@@ -29,6 +29,7 @@
 import android.util.Log;
 
 import org.schabi.newpipe.player.mediasession.MediaSessionPlayerUi;
+import org.schabi.newpipe.player.notification.NotificationPlayerUi;
 import org.schabi.newpipe.util.ThemeHelper;
 
 import java.lang.ref.WeakReference;
@@ -59,6 +60,14 @@ public void onCreate() {
         ThemeHelper.setTheme(this);
 
         player = new Player(this);
+        /*
+        Create the player notification and start immediately the service in foreground,
+        otherwise if nothing is played or initializing the player and its components (especially
+        loading stream metadata) takes a lot of time, the app would crash on Android 8+ as the
+        service would never be put in the foreground while we said to the system we would do so
+         */
+        player.UIs().get(NotificationPlayerUi.class)
+                .ifPresent(NotificationPlayerUi::createNotificationAndStartForeground);
     }
 
     @Override
@@ -68,10 +77,30 @@ public int onStartCommand(final Intent intent, final int flags, final int startI
                     + "], flags = [" + flags + "], startId = [" + startId + "]");
         }
 
+        /*
+        Be sure that the player notification is set and the service is started in foreground,
+        otherwise, the app may crash on Android 8+ as the service would never be put in the
+        foreground while we said to the system we would do so
+        The service is always requested to be started in foreground, so always creating a
+        notification if there is no one already and starting the service in foreground should
+        not create any issues
+        If the service is already started in foreground, requesting it to be started shouldn't
+        do anything
+         */
+        if (player != null) {
+            player.UIs().get(NotificationPlayerUi.class)
+                    .ifPresent(NotificationPlayerUi::createNotificationAndStartForeground);
+        }
+
         if (Intent.ACTION_MEDIA_BUTTON.equals(intent.getAction())
-                && player.getPlayQueue() == null) {
-            // No need to process media button's actions if the player is not working, otherwise the
-            // player service would strangely start with nothing to play
+                && (player == null || player.getPlayQueue() == null)) {
+            /*
+            No need to process media button's actions if the player is not working, otherwise
+            the player service would strangely start with nothing to play
+            Stop the service in this case, which will be removed from the foreground and its
+            notification cancelled in its destruction
+             */
+            stopSelf();
             return START_NOT_STICKY;
         }
 
@@ -87,7 +116,7 @@ public void stopForImmediateReusing() {
             Log.d(TAG, "stopForImmediateReusing() called");
         }
 
-        if (!player.exoPlayerIsNull()) {
+        if (player != null && !player.exoPlayerIsNull()) {
             // Releases wifi & cpu, disables keepScreenOn, etc.
             // We can't just pause the player here because it will make transition
             // from one stream to a new stream not smooth
@@ -98,7 +127,7 @@ public void stopForImmediateReusing() {
     @Override
     public void onTaskRemoved(final Intent rootIntent) {
         super.onTaskRemoved(rootIntent);
-        if (!player.videoPlayerSelected()) {
+        if (player != null && !player.videoPlayerSelected()) {
             return;
         }
         onDestroy();

app/src/main/java/org/schabi/newpipe/player/notification/NotificationPlayerUi.java

@@ -17,23 +17,13 @@
 import org.schabi.newpipe.player.ui.PlayerUi;
 
 public final class NotificationPlayerUi extends PlayerUi {
-    private boolean foregroundNotificationAlreadyCreated = false;
     private final NotificationUtil notificationUtil;
 
     public NotificationPlayerUi(@NonNull final Player player) {
         super(player);
         notificationUtil = new NotificationUtil(player);
     }
 
-    @Override
-    public void initPlayer() {
-        super.initPlayer();
-        if (!foregroundNotificationAlreadyCreated) {
-            notificationUtil.createNotificationAndStartForeground();
-            foregroundNotificationAlreadyCreated = true;
-        }
-    }
-
     @Override
     public void destroy() {
         super.destroy();
@@ -122,4 +112,8 @@ public void onPlayQueueEdited() {
         super.onPlayQueueEdited();
         notificationUtil.createNotificationIfNeededAndUpdate(false);
     }
+
+    public void createNotificationAndStartForeground() {
+        notificationUtil.createNotificationAndStartForeground();
+    }
 }