Fix #15333

`debug.log` with this PR:
```
...
2019-02-03T19:02:35Z Using wallet directory /home/hebasto/.bitcoin/testnet3/wallets
2019-02-03T19:02:35Z init message: Verifying wallet(s)...
2019-02-03T19:02:35Z Using BerkeleyDB version Berkeley DB 4.8.30: (April  9, 2010)
2019-02-03T19:02:35Z Using wallet test_alpha/wallet.dat
2019-02-03T19:02:35Z BerkeleyEnvironment::Open: LogDir=/home/hebasto/.bitcoin/testnet3/wallets/test_alpha/database ErrorFile=/home/hebasto/.bitcoin/testnet3/wallets/test_alpha/db.log
2019-02-03T19:02:35Z Using BerkeleyDB version Berkeley DB 4.8.30: (April  9, 2010)
2019-02-03T19:02:35Z Using wallet alpha_wallet/wallet.dat
2019-02-03T19:02:35Z BerkeleyEnvironment::Open: LogDir=/home/hebasto/.bitcoin/testnet3/wallets/alpha_wallet/database ErrorFile=/home/hebasto/.bitcoin/testnet3/wallets/alpha_wallet/db.log
2019-02-03T19:02:35Z Using BerkeleyDB version Berkeley DB 4.8.30: (April  9, 2010)
2019-02-03T19:02:35Z Using wallet wallet.dat
2019-02-03T19:02:35Z BerkeleyEnvironment::Open: LogDir=/home/hebasto/.bitcoin/testnet3/wallets/database ErrorFile=/home/hebasto/.bitcoin/testnet3/wallets/db.log
2019-02-03T19:02:35Z Using BerkeleyDB version Berkeley DB 4.8.30: (April  9, 2010)
2019-02-03T19:02:35Z Using wallet none/wallet.dat
2019-02-03T19:02:35Z BerkeleyEnvironment::Open: LogDir=/home/hebasto/.bitcoin/testnet3/wallets/none/database ErrorFile=/home/hebasto/.bitcoin/testnet3/wallets/none/db.log
2019-02-03T19:02:35Z init message: Loading banlist...
...
```

ninja check