JDBC artificats should throw SQLException when already closed

In the change to fix JBAS-2741 I mistakenly made the JDBC wrappers throw an SQL
exception if the artifact is already closed. They should just return with an exception.

From the Javadoc:
"Calling the method close on a Statement object that is already closed has no effect."

e.g. In WrappedStatement

public void close() throws SQLException
{
synchronized (lock)

{ if (closed) throw new SQLException("Already closed"); closed = true; }

lc.unregisterStatement(this);
internalClose();
}

this should be:

public void close() throws SQLException
{
synchronized (lock)

{ if (closed) return; closed = true; }

lc.unregisterStatement(this);
internalClose();
}