[presence_dialoginfo] Fix aggregating dialoginfo XML

Fix the looping when aggregating the dialog info XML documents with multiple dialog elements. The xmlUnlinkNode() function inside the loop is breaking the looping (the "next" member is reset).
Credits for reporting and fixing go to Damien Sandras (@dsandras)
Closes #2815

(cherry picked from commit 0cca86f)
(cherry picked from commit 4bc9d96)

modules/presence_dialoginfo/notify_body.c

@@ -109,14 +109,13 @@ str* dlginfo_agg_nbody(str* pres_user, str* pres_domain, str** body_array, int n
 str* agregate_xmls(str* pres_user, str* pres_domain, str** body_array, int n, int partial)
 {
 	int i, j= 0;
-
 	xmlDocPtr  doc = NULL;
 	xmlNodePtr root_node = NULL;
 	xmlNsPtr   namespace = NULL;
-
 	xmlNodePtr p_root= NULL;
 	xmlDocPtr* xml_array ;
 	xmlNodePtr node = NULL;
+	xmlNodePtr next_node = NULL;
 	char *state;
 	int winner_priority = -1, priority ;
 	xmlNodePtr winner_dialog_node = NULL ;
@@ -211,7 +210,8 @@ str* agregate_xmls(str* pres_user, str* pres_domain, str** body_array, int n, in
 				goto error;
 			}
 			if (p_root->children) {
-			for (node = p_root->children; node; node = node->next) {
+			for (node = p_root->children; node; node = next_node) {
+				next_node = node->next;
 				if (node->type == XML_ELEMENT_NODE) {
 					LM_DBG("node type: Element, name: %s\n", node->name);
 					/* we do not copy the node, but unlink it and then add it ot the new node