wallet/chainntfns: prevent sanity check if correctness of birthday block has been verified

In this commit, we prevent any further sanity check attempts by the
wallet if its correctness has previously been verified. We do this to
ensure we don't unnecessarily attempt to find a new candidate.

wallet/chainntfns.go

@@ -360,12 +360,15 @@ func (w *Wallet) birthdaySanityCheck() (*waddrmgr.BlockStamp, error) {
 	}
 
 	// We'll then fetch our wallet's birthday timestamp and block.
-	birthdayTimestamp := w.Manager.Birthday()
+	var (
-	var birthdayBlock waddrmgr.BlockStamp
+		birthdayTimestamp     = w.Manager.Birthday()
+		birthdayBlock         waddrmgr.BlockStamp
+		birthdayBlockVerified bool
+	)
 	err = walletdb.View(w.db, func(tx walletdb.ReadTx) error {
 		var err error
 		ns := tx.ReadBucket(waddrmgrNamespaceKey)
-		birthdayBlock, err = w.Manager.BirthdayBlock(ns)
+		birthdayBlock, birthdayBlockVerified, err = w.Manager.BirthdayBlock(ns)
 		return err
 	})
 
@@ -380,6 +383,17 @@ func (w *Wallet) birthdaySanityCheck() (*waddrmgr.BlockStamp, error) {
 		return nil, err
 	}
 
+	// If the birthday block has already been verified to be correct, we can
+	// exit our sanity check to prevent potentially fetching a better
+	// candidate.
+	if birthdayBlockVerified {
+		log.Debugf("Birthday block has already been verified: "+
+			"height=%d, hash=%v", birthdayBlock.Height,
+			birthdayBlock.Hash)
+
+		return &birthdayBlock, nil
+	}
+
 	log.Debugf("Starting sanity check for the wallet's birthday block "+
 		"from: height=%d, hash=%v", birthdayBlock.Height,
 		birthdayBlock.Hash)
@@ -505,21 +519,15 @@ func (w *Wallet) birthdaySanityCheck() (*waddrmgr.BlockStamp, error) {
 		timestampDelta = birthdayTimestamp.Sub(header.Timestamp)
 	}
 
-	// At this point, we've found a valid candidate that satisfies our
+	// At this point, we've found a new, better candidate, so we'll write it
-	// conditions above. If this is our current birthday block, then we can
+	// to disk.
-	// exit to avoid the additional database transaction.
-	if candidate.Hash.IsEqual(&birthdayBlock.Hash) {
-		return &candidate, nil
-	}
-
-	// Otherwise, we have a new, better candidate, so we'll write it to
-	// disk.
 	log.Debugf("Found a new valid wallet birthday block: height=%d, hash=%v",
 		candidate.Height, candidate.Hash)
 
 	err = walletdb.Update(w.db, func(tx walletdb.ReadWriteTx) error {
 		ns := tx.ReadWriteBucket(waddrmgrNamespaceKey)
-		if err := w.Manager.SetBirthdayBlock(ns, candidate); err != nil {
+		err := w.Manager.SetBirthdayBlock(ns, candidate, true)
+		if err != nil {
 			return err
 		}
 		return w.Manager.SetSyncedTo(ns, &candidate)