[3.0]manage the time to live of the user_data instance of LibVLC Event Callback

manage the time to live of the user_data instance of LibVLC Event Callback.

This prevents access to the released instance in the LibVLC Event Callback and prevents unauthorized access to the released pointer.

The following rare crashes etc. will be fixed.

• libobjc.A.dylib objc_retain
• libobjc.A.dylib objc_msgSend
• libobjc.A.dylib objc_release