chainntnfs/neutrinonotify: fix regression for historical spend dispatches

In this commit, we fix an issue that was recently introduced to the way
we handle historical dispatches for the neutrino notifier. In a recent
change, we no return an error if we’re unable to actually find the
transaction that spends an outpoint. If this is the case, then the
outpoint is actually unspent, and we should proceed as normal.

chainntnfs/neutrinonotify/neutrino.go

@@ -3,6 +3,7 @@ package neutrinonotify
 import (
 	"errors"
 	"fmt"
+	"strings"
 	"sync"
 	"sync/atomic"
 	"time"
@@ -629,7 +630,7 @@ func (n *NeutrinoNotifier) RegisterSpendNtfn(outpoint *wire.OutPoint,
 			Height: int32(heightHint),
 		}),
 	)
-	if err != nil {
+	if err != nil && !strings.Contains(err.Error(), "not found") {
 		return nil, err
 	}