Call DisconnectEvent explicitly instead of relying on ConnectedPlayer#teardown() to do it for us

Should fix (but not verified) #289

proxy/src/main/java/com/velocitypowered/proxy/connection/client/ConnectedPlayer.java

@@ -104,6 +104,7 @@ public class ConnectedPlayer implements MinecraftConnectionAssociation, Player {
   private final CompletableFuture<Void> teardownFuture = new CompletableFuture<>();
 
   private @MonotonicNonNull List<String> serversToTry = null;
+  private boolean explicitlyDisconnected = false;
 
   ConnectedPlayer(VelocityServer server, GameProfile profile, MinecraftConnection connection,
       @Nullable InetSocketAddress virtualHost, boolean onlineMode) {
@@ -281,9 +282,20 @@ public class ConnectedPlayer implements MinecraftConnectionAssociation, Player {
 
   @Override
   public void disconnect(Component reason) {
+    if (connection.eventLoop().inEventLoop()) {
+      disconnect0(reason, false);
+    } else {
+      connection.eventLoop().execute(() -> disconnect0(reason, false));
+    }
+  }
+
+  public void disconnect0(Component reason, boolean duringLogin) {
     logger.info("{} has disconnected: {}", this,
         LegacyComponentSerializer.legacy().serialize(reason));
+    this.explicitlyDisconnected = true;
     connection.closeWith(Disconnect.create(reason));
+
+    server.getEventManager().fireAndForget(new DisconnectEvent(this, duringLogin));
   }
 
   @Override
@@ -574,10 +586,11 @@ public class ConnectedPlayer implements MinecraftConnectionAssociation, Player {
       connectedServer.disconnect();
     }
     boolean isConnected = server.getPlayer(this.getUniqueId()).isPresent();
-
     server.unregisterConnection(this);
-    server.getEventManager().fire(new DisconnectEvent(this, !isConnected))
-            .thenRun(() -> this.teardownFuture.complete(null));
+    if (!this.explicitlyDisconnected) {
+      server.getEventManager().fire(new DisconnectEvent(this, !isConnected))
+          .thenRun(() -> this.teardownFuture.complete(null));
+    }
   }
 
   public CompletableFuture<Void> getTeardownFuture() {

proxy/src/main/java/com/velocitypowered/proxy/connection/client/LoginSessionHandler.java

@@ -204,7 +204,7 @@ public class LoginSessionHandler implements MinecraftSessionHandler {
           inbound.getVirtualHost().orElse(null), onlineMode);
       this.connectedPlayer = player;
       if (!server.canRegisterConnection(player)) {
-        player.disconnect(VelocityMessages.ALREADY_CONNECTED);
+        player.disconnect0(VelocityMessages.ALREADY_CONNECTED, true);
         return CompletableFuture.completedFuture(null);
       }
 
@@ -246,10 +246,10 @@ public class LoginSessionHandler implements MinecraftSessionHandler {
 
           Optional<Component> reason = event.getResult().getReason();
           if (reason.isPresent()) {
-            player.disconnect(reason.get());
+            player.disconnect0(reason.get(), true);
           } else {
             if (!server.registerConnection(player)) {
-              player.disconnect(VelocityMessages.ALREADY_CONNECTED);
+              player.disconnect0(VelocityMessages.ALREADY_CONNECTED, true);
               return;
             }
 
@@ -269,7 +269,7 @@ public class LoginSessionHandler implements MinecraftSessionHandler {
         .thenRunAsync(() -> {
           Optional<RegisteredServer> toTry = event.getInitialServer();
           if (!toTry.isPresent()) {
-            player.disconnect(VelocityMessages.NO_AVAILABLE_SERVERS);
+            player.disconnect0(VelocityMessages.NO_AVAILABLE_SERVERS, true);
             return;
           }
           player.createConnectionRequest(toTry.get()).fireAndForget();