The download-image function in app.media silently succeeded when the
remote image URL was unreachable or returned an error status code,
causing create-file-media-object-from-url to report success with no
actual image stored.
Add exception handling for connection refused, timeouts, and I/O errors
around the HTTP request, and validate the HTTP status code in
parse-and-validate before processing the response body.
Fixes#8499
Signed-off-by: Andrey Antukh <niwi@niwi.nz>