Fix sending PRACK for multiple provisional replies.

Reported by Giuseppe Cardone.

(cherry picked from commit 3cd6db2)

modules/b2b_entities/dlg.c

@@ -2484,16 +2484,15 @@ void b2b_tm_cback(struct cell *t, b2b_table htable, struct tmcb_params *ps)
 				if(leg)
 				{
 					LM_DBG("Found existing leg  - Nothing to update\n");
-					goto done;
-				}
-
-				leg = b2b_add_leg(dlg, msg, &to_tag);
-				if(leg == NULL)
-				{
-					LM_ERR("Failed to add dialog leg\n");
-					goto error;
+				} else {
+					leg = b2b_add_leg(dlg, msg, &to_tag);
+					if(leg == NULL)
+					{
+						LM_ERR("Failed to add dialog leg\n");
+						goto error;
+					}
+					UPDATE_DBFLAG(dlg);
 				}
-				UPDATE_DBFLAG(dlg);
 				/* PRACK handling */
 				/* if the provisional reply contains a Require: 100rel header -> send PRACK */
 				hdr = get_header_by_static_name( msg, "Require");