ethclient: fix tx sender cache miss detection (#23877)

This fixes a bug in TransactionSender where it would return the
zero address for transactions where the sender address wasn't
cached already.

Co-authored-by: Felix Lange <fjl@twurst.com>

ethclient/signer.go

@@ -45,7 +45,7 @@ func (s *senderFromServer) Equal(other types.Signer) bool {
 }
 
 func (s *senderFromServer) Sender(tx *types.Transaction) (common.Address, error) {
-	if s.blockhash == (common.Hash{}) {
+	if s.addr == (common.Address{}) {
 		return common.Address{}, errNotCached
 	}
 	return s.addr, nil