Merge pull request #817 from snen/presentity_dialog_id_null_fix

presence: fix crush if dialog id is NULL

modules/presence/presentity.c

@@ -691,7 +691,7 @@ int update_presentity(struct sip_msg* msg, presentity_t* presentity, str* body,
 			}
 
 			check_if_dialog(*body, &is_dialog, &dialog_id);
-			if (is_dialog == 1) {
+			if ( dialog_id ) {
 				if (delete_presentity_if_dialog_id_exists(presentity, dialog_id) < 0) {
 					goto error;
 				}