Send close datagram when entering closing state

quic/transport/ngtcp2/connection/closingstate.nim

@@ -14,9 +14,16 @@ proc newClosingConnection*(finalDatagram: Datagram, ids: seq[ConnectionId],
   state.init(ids, duration)
   state
 
-{.push locks: "unknown".}
-
-method receive(state: ClosingConnection, datagram: Datagram) =
+proc sendFinalDatagram(state: ClosingConnection) =
   state.connection.outgoing.putNoWait(state.finalDatagram)
 
+{.push locks: "unknown".}
+
+method enter(state: ClosingConnection, connection: QuicConnection) =
+  procCall enter(DrainingConnection(state), connection)
+  state.sendFinalDatagram()
+
+method receive(state: ClosingConnection, datagram: Datagram) =
+  state.sendFinalDatagram()
+
 {.pop.}

quic/transport/ngtcp2/connection/drainingstate.nim

@@ -32,7 +32,7 @@ proc onTimeout(state: DrainingConnection) =
 
 {.push locks: "unknown".}
 
-method enter(state: DrainingConnection, connection: QuicConnection) =
+method enter*(state: DrainingConnection, connection: QuicConnection) =
   state.connection = connection
   state.timeout = newTimeout(proc = state.onTimeout())
   state.timeout.set(state.duration)