nickserv/enforce: do not check if a non-existent user is banned from a channel

modules/nickserv/enforce.c

@@ -309,8 +309,8 @@ static void ns_cmd_regain(sourceinfo_t *si, int parc, char *parv[])
 	}
 	if ((si->smu == mn->owner) || verify_password(mn->owner, password))
 	{
-		if (user_is_channel_banned(si->su, 'b') || user_is_channel_banned(si->su, 'q') ||
-		    user_is_channel_banned(u, 'b') || user_is_channel_banned(u, 'q'))
+		if ((si->su != NULL && user_is_channel_banned(si->su, 'b') || user_is_channel_banned(si->su, 'q')) ||
+		    user_is_channel_banned(u, 'b') || user_is_channel_banned(u, 'q')))
 		{
 			command_fail(si, fault_noprivs, _("You can not regain your nickname while banned or quieted on a channel."));
 			return;