Return early if http client is already closed

[wendigo]

If the query is cancelled the existing code can result in:

presto-worker       | 2024-12-03T20:36:32.663+0545	INFO	page-buffer-client-callback-65	stderr	java.lang.IllegalStateException: client is already marked as completed
presto-worker       | 2024-12-03T20:36:32.663+0545	INFO	page-buffer-client-callback-65	stderr		at com.google.common.base.Preconditions.checkState(Preconditions.java:513)
presto-worker       | 2024-12-03T20:36:32.663+0545	INFO	page-buffer-client-callback-65	stderr		at io.trino.operator.DirectExchangeClient.addPages(DirectExchangeClient.java:333)
presto-worker       | 2024-12-03T20:36:32.663+0545	INFO	page-buffer-client-callback-65	stderr		at io.trino.operator.DirectExchangeClient$ExchangeClientCallback.addPages(DirectExchangeClient.java:427)
presto-worker       | 2024-12-03T20:36:32.663+0545	INFO	page-buffer-client-callback-65	stderr		at io.trino.operator.HttpPageBufferClient$1.onSuccess(HttpPageBufferClient.java:436)
presto-worker       | 2024-12-03T20:36:32.663+0545	INFO	page-buffer-client-callback-65	stderr		at io.trino.operator.HttpPageBufferClient$1.onSuccess(HttpPageBufferClient.java:367)
presto-worker       | 2024-12-03T20:36:32.663+0545	INFO	page-buffer-client-callback-65	stderr		at com.google.common.util.concurrent.Futures$CallbackListener.run(Futures.java:1137)
presto-worker       | 2024-12-03T20:36:32.663+0545	INFO	page-buffer-client-callback-65	stderr		at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1144)
presto-worker       | 2024-12-03T20:36:32.663+0545	INFO	page-buffer-client-callback-65	stderr		at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
presto-worker       | 2024-12-03T20:36:32.663+0545	INFO	page-buffer-client-callback-65	stderr		at java.base/java.lang.Thread.run(Thread.java:1575)

as the in-flight request will try to call addPages while the client was already marked as completed

Description

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## Section
* Fix some things. ({issue}`issuenumber`)