Fixed dialog-info problems in case there is no dialog.

Without that patch, when OpenSIPS does not find any active dialog
and needs to NOTIFY that state, it correctly sends a full state dialog
information, but the XML document is wrong.

This is the wrong format, the one that was used:
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
version="0" state="partial" entity="sip:752@ds.local.beip.be"><dialog
id="752"><state>terminated</state></dialog></dialog-info>
(info is not partiali but full, dialog id is wrong).

This is the correct format:
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
version="6" state="full" entity="sip:753@ds.local.beip.be"/>