asyncAddEntry fails with NPE with LedgerHandler created with createLedgerAdv

[apache]

asyncAddEntry fails with NPE with LedgerHandler created with createLedgerAdv

[eolivelli]

The signature of asyncAddEntry is wrong, it does not throw BKException as it is an async function

public void asyncAddEntry(final long entryId, final byte[] data, final int offset, final int length,
            final AddCallback cb, final Object ctx) throws BKException

Maybe we can fix this error too

[sijie]

@eolivelli can you share the code that cause the NPE?

[eolivelli]

@sijie I have modified the description, the new testcase in PR #244 demostrates the problem