manager: fix memory leak in manager_add_filter function

(closes issue ASTERISK-23420)
Reported by: Etienne Lessard
Patches:
    manager_eventfilter_leak uploaded by Etienne Lessard (license 6394)


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/11@410609 65c4cc65-6c06-0410-ace0-fbb531ad65f3

main/manager.c

@@ -4810,6 +4810,8 @@ static enum add_filter_result manager_add_filter(const char *filter_pattern, str
 		ao2_t_link(whitefilters, new_filter, "link new filter into white user container");
 	}
 
+	ao2_ref(new_filter, -1);
+
 	return FILTER_SUCCESS;
 }