Connector doesn't drop closed connections that are ready to decode

[drewdzzz]

Consider the following patch:

diff --git a/test/ClientTest.cpp b/test/ClientTest.cpp
index e606010..410b624 100644
--- a/test/ClientTest.cpp
+++ b/test/ClientTest.cpp
@@ -293,6 +293,10 @@ many_conn_ping(Connector<BUFFER, NetProvider> &client)
 	client.close(conn1);
 	client.close(conn2);
 	client.close(conn3);
+
+	/** All the connections are closed - we shouldn't get any here. */
+	conn_opt = client.waitAny(WAIT_TIMEOUT);
+	fail_if(conn_opt.has_value());
 }
 
 /** Single connection, errors in response. */

The test fails (with EpollNetProvider, at least) - it happens because ready to decode connections are still referenced by Connector. The fix is quite trivial, but we should investigate the state machine - I'm sure there are more places holding closed connections.