Add synchronized lock to sdlmanager.dispose

Author: joeygrover

android/sdl_android/src/main/java/com/smartdevicelink/managers/SdlManager.java

@@ -216,7 +216,7 @@ public void run() {
      */
     @SuppressLint("NewApi")
     @Override
-    public void dispose() {
+    public synchronized void dispose() {
         if (this.permissionManager != null) {
             this.permissionManager.dispose();
         }