protect against faulty relays that send more than one EOSE halting us

using sync.Once{} to only emit to the EndOfStoredEvents channel once
(it has capacity 1 so anything over that would halt).

relay.go

@@ -140,7 +140,9 @@ func (r *Relay) Connect() error {
 				var channel string
 				json.Unmarshal(jsonMessage[1], &channel)
 				if subscription, ok := r.subscriptions.Load(channel); ok {
-					subscription.EndOfStoredEvents <- struct{}{}
+					subscription.emitEose.Do(func() {
+						subscription.EndOfStoredEvents <- struct{}{}
+					})
 				}
 			case "OK":
 				if len(jsonMessage) < 3 {

subscription.go

@@ -1,5 +1,7 @@
 package nostr
 
+import "sync"
+
 type Subscription struct {
 	id   string
 	conn *Connection
@@ -8,7 +10,8 @@ type Subscription struct {
 	Events            chan Event
 	EndOfStoredEvents chan struct{}
 
-	stopped bool
+	stopped  bool
+	emitEose sync.Once
 }
 
 type EventMessage struct {