Fix TCPServer "Should disconnect client" test

"Should disconnect client" test was failing randomly on Mac CI tests, so
this PR is making it more reliable reading on the closed client instead of
writing to it

tests/core/io/test_tcp_server.h

@@ -85,8 +85,8 @@ Error poll(Ref<StreamPeerTCP> p_client) {
 	const uint64_t time = OS::get_singleton()->get_ticks_usec();
 	Error err = p_client->poll();
 	while (err != Error::OK && (OS::get_singleton()->get_ticks_usec() - time) < MAX_WAIT_USEC) {
-		err = p_client->poll();
 		OS::get_singleton()->delay_usec(SLEEP_DURATION);
+		err = p_client->poll();
 	}
 	return err;
 }
@@ -183,8 +183,8 @@ TEST_CASE("[TCPServer] When stopped shouldn't accept new connections") {
 	time = OS::get_singleton()->get_ticks_usec();
 	Error err = new_client->poll();
 	while (err != Error::OK && err != Error::ERR_CONNECTION_ERROR && (OS::get_singleton()->get_ticks_usec() - time) < MAX_WAIT_USEC) {
-		err = new_client->poll();
 		OS::get_singleton()->delay_usec(SLEEP_DURATION);
+		err = new_client->poll();
 	}
 	REQUIRE((err == Error::OK || err == Error::ERR_CONNECTION_ERROR));
 	StreamPeerTCP::Status status = new_client->get_status();
@@ -210,7 +210,10 @@ TEST_CASE("[TCPServer] Should disconnect client") {
 	server->stop();
 	CHECK_FALSE(server->is_listening());
 
-	client->put_string(hello_world);
+	// Reading for a closed connection will print an error.
+	ERR_PRINT_OFF;
+	CHECK_EQ(client->get_string(), String());
+	ERR_PRINT_ON;
 	REQUIRE_EQ(poll(client), Error::OK);
 	CHECK_EQ(client->get_status(), StreamPeerTCP::STATUS_NONE);
 }