wallet: make sure the bucket is not nil to avoid panic

wallet/chainntfns.go

@@ -6,6 +6,8 @@ package wallet
 
 import (
 	"bytes"
+	"errors"
+	"fmt"
 	"time"
 
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
@@ -24,6 +26,9 @@ const (
 	birthdayBlockDelta = 2 * time.Hour
 )
 
+// ErrEmptyBucket is used when an expected bucket is not found in the database.
+var ErrEmptyBucket = errors.New("empty waddrmgr bucket")
+
 func (w *Wallet) handleChainNotifications() {
 	defer w.wg.Done()
 
@@ -242,6 +247,9 @@ func (w *Wallet) handleChainNotifications() {
 // the passed block.
 func (w *Wallet) connectBlock(dbtx walletdb.ReadWriteTx, b wtxmgr.BlockMeta) error {
 	addrmgrNs := dbtx.ReadWriteBucket(waddrmgrNamespaceKey)
+	if addrmgrNs == nil {
+		return fmt.Errorf("%w: empty waddrmgr bucket", ErrEmptyBucket)
+	}
 
 	bs := waddrmgr.BlockStamp{
 		Height:    b.Height,