Fix infinite loop on s_client starttls xmpp

 * When the host used in "-connect" is not what the remote XMPP server expects
   the server will return an error like this:
     <stream:error>
       <host-unknown xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
     </stream:error>
 * But the actual code will stay on the loop forever because the stop condition
   "/stream:features>" will never happen,
 * Make this more robust: The stop condition should be that BIO_read failed
 * Test if for example with ::

    openssl s_client  -connect random.jabb3r.net:5222 -starttls xmpp