make stream shutdown if self-node has been removed

Currently we will read the node from database, and since it is
deleted, the id might be set to nil. Keep the node around and
just shutdown, so it is cleanly removed from notifier.

Fixes #2118

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

hscontrol/poll.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"math/rand/v2"
 	"net/http"
+	"slices"
 	"sort"
 	"strings"
 	"time"
@@ -273,6 +274,12 @@ func (m *mapSession) serveLongPoll() {
 				return
 			}
 
+			// If the node has been removed from headscale, close the stream
+			if slices.Contains(update.Removed, m.node.ID) {
+				m.tracef("node removed, closing stream")
+				return
+			}
+
 			m.tracef("received stream update: %s %s", update.Type.String(), update.Message)
 			mapResponseUpdateReceived.WithLabelValues(update.Type.String()).Inc()