Observed once in a personal mach5 job.

The test was modified to run with 5 second idle timeout. The connection was closed while the client was still preparing the request headers. The request failed as expected, but the client got stuck in the client.close() call.

To reproduce:
- set a short connection timeout in the test (-Djdk.test.server.quic.idleTimeout=4)
- set a shorter test timeout (the default is 6 minutes)
- add a Thread.sleep(5000) before this line: https://github.com/openjdk/jdk/blob/2d815ac61b437835163d4014bfed16f0f3faea50/src/java.net.http/share/classes/jdk/internal/net/http/Http3Connection.java#L533