Fixed client hang when server don't PUSH (aka the NO_SOUP_FOR_YOU patch)

Fixed client hang when server don't PUSH (aka the NO_SOUP_FOR_YOU patch)

Solves bug ticket 13
<https://community.openvpn.net/openvpn/ticket/13>

When the client sends PUSH_REQUESTS, it waits until the server sends PUSH_REPLY.
If the server do not have anything to push to the client nothing happens.  The
client will then regularly send new PUSH_REQUESTS until it gets an answer, which
results in not completing the connection negotiation.

This patch makes the server send an empty PUSH_REPLY when it has nothing to more
to push to the client.

Signed-off-by: David Sommerseth <dazo@users.sourceforge.net>
Acked-by: James Yonan <james@openvpn.net>