core, eth/downloader: fix ancestor lookup for fast sync

core/rawdb/accessors_chain.go

@@ -271,6 +271,15 @@ func DeleteTd(db DatabaseDeleter, hash common.Hash, number uint64) {
 	}
 }
 
+// HasReceipts verifies the existence of all the transaction receipts belonging
+// to a block.
+func HasReceipts(db DatabaseReader, hash common.Hash, number uint64) bool {
+	if has, err := db.Has(blockReceiptsKey(number, hash)); !has || err != nil {
+		return false
+	}
+	return true
+}
+
 // ReadReceipts retrieves all the transaction receipts belonging to a block.
 func ReadReceipts(db DatabaseReader, hash common.Hash, number uint64) types.Receipts {
 	// Retrieve the flattened receipt slice