Setting RenewTickets does not respect existing cache file settings

Setting `RenewTickets` seems to "forget" cache configuration of the client and revert back to default cache location. Code used:

```csharp
var client = new KerberosClient(config, loggerFactory);
client.CacheInMemory = false;
client.Cache = new Krb5TicketCache(options.CacheFile);
client.RenewTickets = true;
```

after the last line runs, the cache is no longer pointing to what is specified in `options.CacheFile`.