Handle log and report download errors in UI

[mmurto]

          > Looks like the UI is not handling the error correctly and writing the error response to the file. @mmurto Is it even possible to improve that with the way downloads are currently implemented or does this depend on #178?

Doesn't depend on it - this does not throw when the API returns an error code as the fetch succeeds, so it should be modified to throw and display an error in the UI if the response status in not 2xx.

Originally posted by @mmurto in #1415 (comment)

The same should be done for report downloads in addition to logs.