Make a copy of the players list when disconnecting them all on shutdown (#928)

connector/src/main/java/org/geysermc/connector/GeyserConnector.java

@@ -61,6 +61,7 @@ import org.geysermc.connector.utils.LocaleUtils;
 import java.net.InetSocketAddress;
 import java.text.DecimalFormat;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.List;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.Executors;
@@ -189,7 +190,9 @@ public class GeyserConnector {
         if (players.size() >= 1) {
             bootstrap.getGeyserLogger().info(LanguageUtils.getLocaleStringLog("geyser.core.shutdown.kick.log", players.size()));
 
-            for (GeyserSession playerSession : players) {
+            // Make a copy to prevent ConcurrentModificationException
+            final List<GeyserSession> tmpPlayers = new ArrayList<>(players);
+            for (GeyserSession playerSession : tmpPlayers) {
                 playerSession.disconnect(LanguageUtils.getPlayerLocaleString("geyser.core.shutdown.kick.message", playerSession.getClientData().getLanguageCode()));
             }