guard against document.location being null or undefined

[mattrobenolt]

fixes #356

[mattrobenolt]

@pkaminski do you think this is reasonable? Not sure if it'd make sense to put something in http.url as the fallback, like <unknown>.

[pkaminski]

Seems reasonable to me, assuming that nothing bad happens in Sentry when the field isn't set. Since the condition happens very rarely I don't think it's worth overthinking this -- just make sure it doesn't crash and take the original exception with it. 😄

[dcramer]

imo delete http -- id prefer not to allow an optional http url, even if we do today (we may not im not sure)