Ensure dispose is run in close if needed

If close is being run when the pcb is nulled, and we find an event on
the queue, run dispose.  This catches cases where fin or error is
pending.

Author: willmmiles

src/AsyncTCP.cpp

@@ -253,7 +253,7 @@ static inline lwip_tcp_event_packet_t *_get_async_event() {
   }
 }
 
-static void _remove_events_for_client(AsyncClient *client) {
+static size_t _remove_events_for_client(AsyncClient *client) {
   lwip_tcp_event_packet_t *removed_event_chain;
   {
     queue_mutex_guard guard;
@@ -269,6 +269,7 @@ static void _remove_events_for_client(AsyncClient *client) {
     removed_event_chain = t->next;
     _free_event(t);
   }
+  return count;
 };
 
 void AsyncTCP_detail::handle_async_event(lwip_tcp_event_packet_t *e) {
@@ -637,7 +638,9 @@ static err_t _tcp_close_api(struct tcpip_api_call_data *api_call_msg) {
     *msg->pcb = nullptr;  // PCB is now the property of LwIP
   } else {
     // Ensure there is not an error event queued for this client
-    _remove_events_for_client(msg->close);
+    if (_remove_events_for_client(msg->close)) {
+      msg->err = ERR_OK;  // dispose needs to be run
+    }
   }
   return msg->err;
 }