fix: delete addrs when "updating" them to zero

1. Fix expiration check to check "not before" instead of after.
Otherwise, something that is expiring "now" won't count as expired. The
datastore-backed peerstore already had the correct logic.
2. Short-circuit updating the TTL to 0 and just delete the records.

Note: this wasn't causing problems on Linux (likely due to monotonic
clocks?) but was causing go-libp2p tests to fail reliably on Windows.

pstoremem/addr_book.go

@@ -25,7 +25,7 @@ type expiringAddr struct {
 }
 
 func (e *expiringAddr) ExpiredBy(t time.Time) bool {
-	return t.After(e.Expires)
+	return !t.Before(e.Expires)
 }
 
 type peerRecordState struct {
@@ -315,9 +315,15 @@ func (mab *memoryAddrBook) UpdateAddrs(p peer.ID, oldTTL time.Duration, newTTL t
 	defer s.Unlock()
 	exp := time.Now().Add(newTTL)
 	amap, found := s.addrs[p]
-	if found {
-		for k, a := range amap {
-			if oldTTL == a.TTL {
+	if !found {
+		return
+	}
+
+	for k, a := range amap {
+		if oldTTL == a.TTL {
+			if newTTL == 0 {
+				delete(amap, k)
+			} else {
 				a.TTL = newTTL
 				a.Expires = exp
 				amap[k] = a

test/addr_book_suite.go

@@ -210,6 +210,18 @@ func testUpdateTTLs(m pstore.AddrBook) func(t *testing.T) {
 			m.UpdateAddrs(id, time.Hour, time.Minute)
 		})
 
+		t.Run("update to 0 clears addrs", func(t *testing.T) {
+			id := GeneratePeerIDs(1)[0]
+			addrs := GenerateAddrs(1)
+
+			// Shouldn't panic.
+			m.SetAddrs(id, addrs, time.Hour)
+			m.UpdateAddrs(id, time.Hour, 0)
+			if len(m.Addrs(id)) != 0 {
+				t.Error("expected no addresses")
+			}
+		})
+
 		t.Run("update ttls successfully", func(t *testing.T) {
 			ids := GeneratePeerIDs(2)
 			addrs1, addrs2 := GenerateAddrs(2), GenerateAddrs(2)