Fix eth_getBlockReceipts (#2295)

Updated the api method to take into account the celo block receipt.

There was previous confusion around whether eth_getBlockReceipts was
working or not, as it had worked for some people but not others.

This confusion was caused because block receipts are only added when logs
have been generated by system calls. Before gingerbread, we would update
the gas price minimum on every block and hence create a log for the update,
but post gingerbread the only updates that are happening are for epoch blocks.

Co-authored-by: Paul Lange <palango@users.noreply.github.com>

internal/ethapi/api.go

@@ -837,15 +837,21 @@ func (s *PublicBlockChainAPI) GetBlockReceipts(ctx context.Context, blockNrOrHas
 		return nil, err
 	}
 	txs := block.Transactions()
-	if len(txs) != len(receipts) {
+	// We need to account for the block receipt, which if present will mean
+	// that there is one more receipt than transactions.
+	if len(txs) != len(receipts) && len(txs)+1 != len(receipts) {
 		return nil, fmt.Errorf("receipts length mismatch: %d vs %d", len(txs), len(receipts))
 	}
 
 	// Derive the sender.
 	signer := types.MakeSigner(s.b.ChainConfig(), block.Number())
 	result := make([]map[string]interface{}, len(receipts))
 	for i, receipt := range receipts {
-		result[i], err = generateReceiptResponse(ctx, s.b, receipt, signer, txs[i], block.Hash(), block.NumberU64(), uint64(i))
+		var tx *types.Transaction
+		if i < len(txs) {
+			tx = txs[i]
+		}
+		result[i], err = generateReceiptResponse(ctx, s.b, receipt, signer, tx, block.Hash(), block.NumberU64(), uint64(i))
 		if err != nil {
 			return nil, err
 		}