Calling `login` sometimes fails for a user until OpenMonero is restarted
I'm testing against a long-running stagenet instance of OpenMonero using the `devel` branch. At times, a user won't be able to call the `login` endpoint successfully and will be locked out until OpenMonero is restarted. Previously, the address/viewkey was able to log in just fine. 

Here's the request:

```
curl  -w "\n" -X POST http://localhost:1984/login -d '{"address":"REDACTED","view_key":"REDACTED","create_account":true,"generated_locally":true,"withCredentials":false}'
```

The response: 

```
{"reason":"Account creation failed","status":"error"}
```

Relevant lines from OM's log:

```
2019-06-08 14:48:19,698 [I,OM,OpenMoneroRequests.cpp:boost::optional<xmreg::XmrAccount> xmreg::OpenMoneroRequests::select_account(const string&, const string&, bool) const:2186] 5AUYJP: address does not exists
2019-06-08 14:48:19,700 [E,OM,OpenMoneroRequests.cpp:boost::optional<xmreg::XmrAccount> xmreg::OpenMoneroRequests::create_account(const string&, const string&, bool) const:2161] 5AUYJP: account creation failed
```

A restart of OpenMonero produces a successful response with the same request:

```
{"generated_locally":false,"new_address":false,"start_height":0,"status":"success"}
```