Handle Zendesk timeouts without segfaults

[TylerConlee]

time="2018-04-23T13:38:54Z" level=error msg="Error reaching Zendesk" error="Get https://circleci.zendesk.com/api/v2/incremental/tickets.json?include=slas&start_time=1524058674: net/http: request canceled (Client.Timeout exceeded while awaiting headers)" module=zendesk

After this issue, Slab attempts to parse data from that call. Because there's no data, a segfault occurs. It shouldn't.