Add a lock to foreground check

Author: JulianKast

android/sdl_android/src/main/java/com/smartdevicelink/transport/SdlRouterService.java

@@ -3912,10 +3912,12 @@ public void clear() {
     @TargetApi(11)
     @SuppressLint("NewApi")
     private void notifySppError() {
-        // Check first to see if the RouterService is in the Foreground
-        // This is to prevent the notification appearing in error
-        if (!this.isForeground) {
-            return;
+        synchronized (FOREGROUND_NOTIFICATION_LOCK) {
+            // Check first to see if the RouterService is in the Foreground
+            // This is to prevent the notification appearing in error
+            if (!this.isForeground) {
+                return;
+            }
         }
         Notification.Builder builder;
         if (android.os.Build.VERSION.SDK_INT < Build.VERSION_CODES.O) {