Calling `waitAny` after workload can break Tntcxx

[drewdzzz]

Consider the following test case for client:

template <class BUFFER, class NetProvider>
void
test_case(Connector<BUFFER, NetProvider> &client)
{
	TEST_INIT(0);
	Connection<Buf_t, NetProvider> conn1(client);
	Connection<Buf_t, NetProvider> conn2(client);
	Connection<Buf_t, NetProvider> conn3(client);
	int rc = test_connect(client, conn1, localhost, port);
	fail_unless(rc == 0);
	/* Try to connect to the same port */
	rc = test_connect(client, conn2, localhost, port);
	fail_unless(rc == 0);
	rc = test_connect(client, conn3, localhost, port);
	fail_unless(rc == 0);
	rid_t f1 = conn1.ping();
	rid_t f2 = conn2.ping();
	rid_t f3 = conn3.ping();

	/* Wait for all connections. */
	fail_unless(client.wait(conn1, f1, WAIT_TIMEOUT) == 0);
	fail_unless(conn1.futureIsReady(f1));
	fail_unless(conn1.getResponse(f1).header.code == 0);

	fail_unless(client.wait(conn2, f2, WAIT_TIMEOUT) == 0);
	fail_unless(conn2.futureIsReady(f2));
	fail_unless(conn2.getResponse(f2).header.code == 0);

	fail_unless(client.wait(conn3, f3, WAIT_TIMEOUT) == 0);
	fail_unless(conn3.futureIsReady(f3));
	fail_unless(conn3.getResponse(f3).header.code == 0);

	/* Wait any. */
	std::optional<Connection<Buf_t, NetProvider>> conn_opt = client.waitAny(WAIT_TIMEOUT);

	/* Close all connections. */
	client.close(conn1);
	client.close(conn2);
	client.close(conn3);
}

The test fails with the following assertion (LibevNetProvider is used):

Assertion failed: (hasDataToDecode(conn)), function waitAny, file Connector.hpp, line 274.

Note that if you leave only one connection, the test will pass successfully.