ethclient: simplify error handling in TransactionReceipt (#28748)

Co-authored-by: Martin HS <martin@swende.se>
Co-authored-by: Felix Lange <fjl@twurst.com>

ethclient/ethclient.go

@@ -307,10 +307,8 @@ func (ec *Client) TransactionInBlock(ctx context.Context, blockHash common.Hash,
 func (ec *Client) TransactionReceipt(ctx context.Context, txHash common.Hash) (*types.Receipt, error) {
 	var r *types.Receipt
 	err := ec.c.CallContext(ctx, &r, "eth_getTransactionReceipt", txHash)
-	if err == nil {
-		if r == nil {
-			return nil, ethereum.NotFound
-		}
+	if err == nil && r == nil {
+		return nil, ethereum.NotFound
 	}
 	return r, err
 }