OPS-951 Fix bug in Novell LDAP connector that can cause a thread to crash because of an unhandled exception.

* remove the ifdef so we catch ObjectDisposedException.  This can happen if the connection is closed while the reader thread is performing a read operation.

We ship our own version of Novell.Diretory.Ldap.dll in deki's src/redist so this pull isn't really necessary.  I'll also submit a bug/patch upstream.