res_pjsip: Don't assume a request will have any addresses.

When performing DNS resolution the failover code present in
res_pjsip currently assumes that a request will always have
at least one viable address. In practice this is not true.
A domain may be used that has no records.

The code now checks that at least one address exists on the
request which prevents looping.

ASTERISK-26364 #close

Change-Id: Ic0761b0264864acd85915c94d878a81624940f4c

res/res_pjsip.c

@@ -3584,7 +3584,7 @@ int ast_sip_failover_request(pjsip_tx_data *tdata)
 {
 	pjsip_via_hdr *via;
 
-	if (tdata->dest_info.cur_addr == tdata->dest_info.addr.count - 1) {
+	if (!tdata->dest_info.addr.count || (tdata->dest_info.cur_addr == tdata->dest_info.addr.count - 1)) {
 		/* No more addresses to try */
 		return 0;
 	}