Fix memory leak in OpenSslEngine

Motivation:

When a remote peer did open a connection and only do the handshake without sending any data and then directly close the connection we did not call shutdown() in the OpenSslEngine. This leads to a native memory leak. Beside this it also was not fireed when a OpenSslEngine was created but never used.

Modifications:

- Make sure shutdown() is called in all cases when closeInbound() is called
- Call shutdown() also in the finalize() method to ensure we release native memory when the OpenSslEngine is GC'ed

Result:

No more memory leak when using OpenSslEngine