fix help XP leaderboard with non-members

src/main/java/net/discordjug/javabot/systems/user_commands/leaderboard/ExperienceLeaderboardSubcommand.java

@@ -162,7 +162,7 @@ public void handleButton(@NotNull ButtonInteractionEvent event, Button button) {
 	}
 
 	private UserData createUserData(Guild guild, Integer position, double experience, long userId, String prefix) {
-		Member member = guild.retrieveMemberById(userId).complete();
+		Member member = guild.retrieveMemberById(userId).onErrorMap(e -> null).complete();
 		String displayName;
 		if (member == null) {
 			displayName = String.valueOf(userId);