Bitflyer: fix futures market without alias
Bitflyer: fix futures market without alias

```
bitflyer GET https://api.bitflyer.com/v1/getmarkets

[
  { product_code: 'BTC_JPY', market_type: 'Spot' },
	{ product_code: 'XRP_JPY', market_type: 'Spot' },
	{ product_code: 'ETH_JPY', market_type: 'Spot' },
	{ product_code: 'XLM_JPY', market_type: 'Spot' },
	{ product_code: 'MONA_JPY', market_type: 'Spot' },
	{ product_code: 'ETH_BTC', market_type: 'Spot' },
	{ product_code: 'BCH_BTC', market_type: 'Spot' },
	{ product_code: 'FX_BTC_JPY', market_type: 'FX' },
	{ product_code: 'BTCJPY11MAR2022', market_type: 'Futures' }, 🔴 <<<<<<<<<<<<<<<<<
	{ product_code: 'BTCJPY18MAR2022', alias: 'BTCJPY_MAT1WK', market_type: 'Futures' },
	{ product_code: 'BTCJPY25MAR2022', alias: 'BTCJPY_MAT2WK', market_type: 'Futures' },
	{ product_code: 'BTCJPY24JUN2022', alias: 'BTCJPY_MAT3M', market_type: 'Futures' },
];
```;

results in:
Cannot read properties of undefined (reading 'split')
at Bitflyer.fetchMarkets (.../node_modules/ccxt/js/bitflyer.js:184:42
ccxt/ccxt,ccxt/ccxt,ccxt/ccxt,ccxt/ccxt,ccxt/ccxt