Retrying webfont fetching should continue only when fetchFont() succeeds

ResourceFetcher::fetchFont() may fail. If it fails, we should finish
fetching webfont immediately.

BUG=363517

Review URL: https://codereview.chromium.org/238683005

git-svn-id: svn://svn.chromium.org/blink/trunk@171824 bbb929c8-8fbe-4397-9dbb-9b2b20218538