Leave a server at once instead of waiting for the reader thread

On Windows a socket shutdown doesn't wake a read already waiting, so Disconnect froze the window until the server closed the connection. Vanilla closes the connection and moves on.

crates/horizon-client/src/net.rs

@@ -262,13 +262,15 @@ impl Session {
             w.shutdown();
         }
     }
+    /// `Connection.disconnect`: the socket closes and the game goes on at once.
+    /// The reader thread is left to end on its own: on Windows a shutdown
+    /// doesn't wake a read already waiting, so joining it held the window until
+    /// the server dropped the connection, many seconds later.
     pub fn disconnect(&mut self) {
         if let Some(w) = self.writer.lock().unwrap().take() {
             w.shutdown();
         }
-        if let Some(t) = self.thread.take() {
-            let _ = t.join();
-        }
+        drop(self.thread.take());
     }
 }
 impl Drop for Session {