fix: forward player loaded packet to backend server (#1862)

Return false after handling ServerboundPlayerLoadedPacket so Velocity's normal forwarding path sends the packet to the backend server.

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

@@ -254,7 +254,7 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
       serverConnection.setClientLoaded(true);
       server.getEventManager().fireAndForget(new PlayerClientLoadedWorldEvent(player));
     }
-    return true;
+    return false;
   }
 
   @Override