MT#57820 fix possible NULL deref

Don't attempt to send packets to an endpoint address that is empty and
hasn't been initialised.

Change-Id: Iabeb034ebfc56fc49083c6a10a85b92c6983eebc
(cherry picked from commit 850a1a582e)

daemon/dtls.c

@@ -864,7 +864,7 @@ int dtls(struct stream_fd *sfd, const str *s, const endpoint_t *fsin) {
 
 		if (!fsin) {
 			fsin = &ps->endpoint;
-			if (fsin->port == 9)
+			if (fsin->port == 9 || fsin->address.family == NULL)
 				fsin = NULL;
 		}