Client stall if application close during handshake

Similar to https://github.com/cloudflare/quiche/issues/1118

If the client performs an app-close before sending the `ACK` on *server-HANDSHAKE*, the client seems to stall.

Note the `connection.close()` is invoked (from the client point of view) after handshake is completed (that is, `is_established() == true`).

### Step to reproduce

1. Modify example-client

Set app-close as soon as `is_established`, but before flush egress (`send`)

```
--- a/quiche/examples/client.rs
+++ b/quiche/examples/client.rs
@@ -198,6 +198,10 @@ fn main() {

// Send an HTTP request as soon as the connection is established.
if conn.is_established() && !req_sent {
+ if conn.local_error().is_none() {
+ conn.close(true, 0, b"bye").unwrap();
+ }
+
info!("sending HTTP request for {}", url.path());

let req = format!("GET {}\r\n", url.path());
```

2. Analyze traffic

```
8.374214809 Client -> Server QUIC 1242 Initial, DCID=877468521020d228e9f79e5cb03bd298, SCID=1920bdcce00b65ca1c1da20f38a516cf4dd44d12, PKN: 0, CRYPTO
8.374273705 Server-> Client QUIC 131 Retry, DCID=1920bdcce00b65ca1c1da20f38a516cf4dd44d12, SCID=c23440bd880a991669e36e9e7da9f09588f6e128
8.374509771 Client -> Server QUIC 1242 Initial, DCID=c23440bd880a991669e36e9e7da9f09588f6e128, SCID=1920bdcce00b65ca1c1da20f38a516cf4dd44d12, PKN: 1, CRYPTO
8.376257575 Server-> Client QUIC 1242 Handshake, DCID=1920bdcce00b65ca1c1da20f38a516cf4dd44d12, SCID=c23440bd880a991669e36e9e7da9f09588f6e128
8.376264956 Server-> Client QUIC 353 Handshake, DCID=1920bdcce00b65ca1c1da20f38a516cf4dd44d12, SCID=c23440bd880a991669e36e9e7da9f09588f6e128

/// Client here should reply with ACKs + CRYPTO finish + Connection Close

9.376485690 Server-> Client QUIC 1242 Initial, DCID=1920bdcce00b65ca1c1da20f38a516cf4dd44d12, SCID=c23440bd880a991669e36e9e7da9f09588f6e128, PKN: 1, ACK, CRYPTO
10.375731458 Server-> Client QUIC 1242 Handshake, DCID=1920bdcce00b65ca1c1da20f38a516cf4dd44d12, SCID=c23440bd880a991669e36e9e7da9f09588f6e128
10.375781019 Server-> Client QUIC 186 Handshake, DCID=1920bdcce00b65ca1c1da20f38a516cf4dd44d12, SCID=c23440bd880a991669e36e9e7da9f09588f6e128
13.373703361 Server-> Client QUIC 1242 Initial, DCID=1920bdcce00b65ca1c1da20f38a516cf4dd44d12, SCID=c23440bd880a991669e36e9e7da9f09588f6e128, PKN: 2, ACK, CRYPTO
13.373801916 Server-> Client QUIC 1242 Initial, DCID=1920bdcce00b65ca1c1da20f38a516cf4dd44d12, SCID=c23440bd880a991669e36e9e7da9f09588f6e128, PKN: 3, ACK, PING
```

---

App-Close cannot be sent on `HANDSHAKE` epoch, but because progress is inhibited by `local_error` in `send_single`.