acc: Fix incorrect Request-URI handling

If the config script does not include any Request-URI altering logic
(e.g. no lookup() or $ru manipulation), the acc module would incorrectly fill
in a "msg->new_uri" field which should NOT be freed into the SIP request
structure, leading to the memory pool being corrupted upon transaction release.

Credits to Guillaume Lacroix for reporting

(cherry picked from commit 02cb9f0)

modules/acc/acc_logic.c

@@ -481,7 +481,7 @@ static inline void on_missed(struct cell *t, struct sip_msg *req,
 	 */
 	reset_acc_flag( req, flags_to_reset );
 
-	if (new_uri_bk.s) {
+	if (t->nr_of_outgoings) {
 		req->new_uri = new_uri_bk;
 		req->dst_uri = dst_uri_bk;
 		req->parsed_uri_ok = 0;