AppCache: fix a browser crashing bug that can happen during updates.

BUG=558589

Review URL: https://codereview.chromium.org/1463463003

Cr-Commit-Position: refs/heads/master@{#360967}
void  AppCacheUpdateJob::URLFetcher::OnWriteComplete(int result) {
  if (result < 0) {
    request_->Cancel();
    result_ = DISKCACHE_ERROR;
    OnResponseCompleted();
    return;
  }
  ReadResponseData();
}

void  AppCacheUpdateJob::URLFetcher::OnWriteComplete(int result) {
  if (result < 0) {
    request_->Cancel();
    result_ = DISKCACHE_ERROR;
    OnResponseCompleted();
    return;
  }
  ReadResponseData();
}
