Make sure the client has time to respond to the player info packet.

Apparently, Minecraft 1.13 can take a little too long to respond to
Velocity's player info forwarding packet. This especially noticeable in
offline mode: by the time the client does respond, Velocity has already
completed the login process and tried connecting to the server (it is
very quick under offline mode).

Noticed by Leymooo.

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

@@ -42,7 +42,23 @@ public class LoginSessionHandler implements MinecraftSessionHandler {
     }
 
     @Override
-    public void activated() {
+    public void handle(MinecraftPacket packet) {
+        if (packet instanceof LoginPluginResponse) {
+            LoginPluginResponse lpr = (LoginPluginResponse) packet;
+            if (lpr.getId() == playerInfoId) {
+                if (lpr.isSuccess()) {
+                    // Uh oh, someone's trying to run Velocity behind Velocity. We don't want that happening.
+                    inbound.closeWith(Disconnect.create(
+                            TextComponent.of("Running Velocity behind Velocity isn't supported.", TextColor.RED)
+                    ));
+                } else {
+                    // Proceed with the regular login process.
+                    initiateLogin();
+                }
+            }
+        } else if (packet instanceof ServerLogin) {
+            this.login = (ServerLogin) packet;
+
             if (inbound.getProtocolVersion() >= ProtocolConstants.MINECRAFT_1_13) {
                 LoginPluginMessage message = new LoginPluginMessage();
                 playerInfoId = ThreadLocalRandom.current().nextInt();
@@ -50,30 +66,8 @@ public class LoginSessionHandler implements MinecraftSessionHandler {
                 message.setChannel(VelocityConstants.VELOCITY_IP_FORWARDING_CHANNEL);
                 message.setData(Unpooled.EMPTY_BUFFER);
                 inbound.write(message);
-        }
-    }
-
-    @Override
-    public void handle(MinecraftPacket packet) {
-        if (packet instanceof LoginPluginResponse) {
-            LoginPluginResponse lpr = (LoginPluginResponse) packet;
-            if (lpr.getId() == playerInfoId && lpr.isSuccess()) {
-                // Uh oh, someone's trying to run Velocity behind Velocity. We don't want that happening.
-                inbound.closeWith(Disconnect.create(
-                        TextComponent.of("Running Velocity behind Velocity isn't supported.", TextColor.RED)
-                ));
-            }
-        } else if (packet instanceof ServerLogin) {
-            this.login = (ServerLogin) packet;
-
-            if (VelocityServer.getServer().getConfiguration().isOnlineMode()) {
-                // Request encryption.
-                EncryptionRequest request = generateRequest();
-                this.verify = Arrays.copyOf(request.getVerifyToken(), 4);
-                inbound.write(request);
             } else {
-                // Offline-mode, don't try to request encryption.
+                initiateLogin();
-                handleSuccessfulLogin(GameProfile.forOfflinePlayer(login.getUsername()));
             }
         } else if (packet instanceof EncryptionResponse) {
             try {
@@ -119,6 +113,18 @@ public class LoginSessionHandler implements MinecraftSessionHandler {
         }
     }
 
+    private void initiateLogin() {
+        if (VelocityServer.getServer().getConfiguration().isOnlineMode()) {
+            // Request encryption.
+            EncryptionRequest request = generateRequest();
+            this.verify = Arrays.copyOf(request.getVerifyToken(), 4);
+            inbound.write(request);
+        } else {
+            // Offline-mode, don't try to request encryption.
+            handleSuccessfulLogin(GameProfile.forOfflinePlayer(login.getUsername()));
+        }
+    }
+
     private EncryptionRequest generateRequest() {
         byte[] verify = new byte[4];
         ThreadLocalRandom.current().nextBytes(verify);