Currently server.py --rietveld-issue will crash if there are any
unstarted trybots on the latest patch. Instead of crashing, warn
that the bot hasn't started yet.
Review URL: https://codereview.chromium.org/
758793003
logging.info('Fetching issue %s patch %s try %s...' %
(self._issue, patchset, try_builder))
build_url = try_job_result.get('url', '<bad url>')
+ if build_url is None:
+ logging.warning('Builder %s has not started.' % (try_builder,))
+ continue
gm_upload_output_url = build_url + urllib2.quote(upload_gm_step_url)
logging.info('Fetching %s ...' % (gm_upload_output_url,))