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

apps/s_client.c

@@ -1676,9 +1676,11 @@ SSL_set_tlsext_status_ids(con, ids);
 		while (!strstr(mbuf, "<starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'") &&
 				!strstr(mbuf, "<starttls xmlns=\"urn:ietf:params:xml:ns:xmpp-tls\""))
 			{
-			if (strstr(mbuf, "/stream:features>"))
-				goto shut;
 			seen = BIO_read(sbio,mbuf,BUFSIZZ);
+
+			if (seen <= 0)
+				goto shut;
+
 			mbuf[seen] = 0;
 			}
 		BIO_printf(sbio, "<starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>");