Do not run try workflow when no tasks is found

[La0]

To avoid this crash : https://tools.taskcluster.net/groups/ddpL7pJhTe-RD3SuoplcGQ/tasks/ddpL7pJhTe-RD3SuoplcGQ/runs/0/logs/public%2Flogs%2Flive.log

[marco-c]

Log:

[taskcluster 2019-07-19 14:38:26.263Z] Task ID: ddpL7pJhTe-RD3SuoplcGQ
[taskcluster 2019-07-19 14:38:26.263Z] Worker ID: i-0c9f8146c5866da85
[taskcluster 2019-07-19 14:38:26.263Z] Worker Group: us-east-1
[taskcluster 2019-07-19 14:38:26.263Z] Worker Node Type: m5.xlarge
[taskcluster 2019-07-19 14:38:26.263Z] Worker Type: releng-svc-memory
[taskcluster 2019-07-19 14:38:26.263Z] Public IP: 54.81.162.244
[taskcluster 2019-07-19 14:38:26.263Z] using cache "services-production-code-coverage-bot" -> /cache

2a7d49900151 - Started downloading
2a7d49900151 - Downloaded in 5.613 seconds
Digest: sha256:3981c9809cd004f9b8f794f94b37cefc7da81e3e2a78f5d57dbbc5d9dec70173
Status: Downloaded newer image for mozillareleng/services:docker-image-python3.7-mozilla-codecoverage-bot-1.0.0-x9qb94wdlri5d8ig9ymggb856fac23yj
[taskcluster 2019-07-19 14:39:06.182Z] === Task Starting ===
2019-07-19 14:39.07 Using taskcluster credentials from environment
2019-07-19 14:39.07 Taskcluster Proxy enabled      url=http://172.17.0.2
2019-07-19 14:39.08 Loaded Taskcluster secret      name=repo:github.com/mozilla-releng/services:branch:production
�[37m2019-07-19 14:39:08.046225 [INFO    ] code_coverage_bot.codecov: Mercurial revision (revision='c5f047dfd7a16834a9f803cbdc89094d0867ba5f')�[39;49;00m
�[37m2019-07-19 14:39:14.490880 [INFO    ] code_coverage_bot.artifacts: Downloading artifacts from 0 tasks�[39;49;00m
�[37m2019-07-19 14:39:14.492853 [INFO    ] code_coverage_bot.artifacts: Code coverage artifacts downloaded�[39;49;00m
�[37m2019-07-19 14:45:40.301503 [INFO    ] code_coverage_bot.codecov: https://hg.mozilla.org/try cloned�[39;49;00m
�[37m2019-07-19 14:45:40.307264 [INFO    ] code_coverage_bot.utils: Command failed with code: 1 (command='grcov -t coveralls --service-name TaskCluster --commit-sha COMMIT_SHA --token TOKEN --service-job-number 1 --service-number SERVICE_NUMBER -s /cache/try --ignore-not-existing' output=b'' error=b'error: The following required arguments were not provided:\n    <paths>...\n\nUSAGE:\n    grcov <paths>... --commit-sha <COMMIT HASH> --ignore-not-existing --output-type <OUTPUT TYPE> --service-job-number <SERVICE JOB NUMBER> --service-name <SERVICE NAME> --service-number <SERVICE NUMBER> --source-dir <DIRECTORY> --threads <NUMBER> --token <TOKEN>\n\nFor more information try --help\n')�[39;49;00m
�[31;01m2019-07-19 14:45:40.307898 [ERROR   ] code_coverage_bot.grcov: Error while running grcov�[39;49;00m
Traceback (most recent call last):
  File "/nix/store/zdvmj19bv5vsh8ax55lsj23p4ybzb71p-python3.7-mozilla-codecoverage-bot-1.0.0/bin/..code-coverage-bot-wrapped-wrapped", line 11, in <module>
    sys.exit(main())
  File "/nix/store/zdvmj19bv5vsh8ax55lsj23p4ybzb71p-python3.7-mozilla-codecoverage-bot-1.0.0/lib/python3.7/site-packages/code_coverage_bot/cli.py", line 71, in main
    c.go()
  File "/nix/store/zdvmj19bv5vsh8ax55lsj23p4ybzb71p-python3.7-mozilla-codecoverage-bot-1.0.0/lib/python3.7/site-packages/code_coverage_bot/codecov.py", line 236, in go
    self.go_from_trigger_try()
  File "/nix/store/zdvmj19bv5vsh8ax55lsj23p4ybzb71p-python3.7-mozilla-codecoverage-bot-1.0.0/lib/python3.7/site-packages/code_coverage_bot/codecov.py", line 191, in go_from_trigger_try
    token='TOKEN',
  File "/nix/store/zdvmj19bv5vsh8ax55lsj23p4ybzb71p-python3.7-mozilla-codecoverage-bot-1.0.0/lib/python3.7/site-packages/code_coverage_bot/grcov.py", line 34, in report
    return run_check(cmd)
  File "/nix/store/zdvmj19bv5vsh8ax55lsj23p4ybzb71p-python3.7-mozilla-codecoverage-bot-1.0.0/lib/python3.7/site-packages/code_coverage_bot/utils.py", line 80, in run_check
    raise RunException(f'`{command[0]}` failed with code: {proc.returncode}.')
code_coverage_bot.utils.RunException: `grcov` failed with code: 1.
Sentry is attempting to send 2 pending error messages
Waiting up to 10 seconds
Press Ctrl-C to quit
[taskcluster 2019-07-19 14:45:43.862Z] === Task Finished ===
[taskcluster 2019-07-19 14:45:43.928Z] Artifact "public/chunk_mapping.tar.xz" not found at "/chunk_mapping.tar.xz"
[taskcluster 2019-07-19 14:45:43.991Z] Artifact "public/zero_coverage_report.json" not found at "/zero_coverage_report.json"
[taskcluster 2019-07-19 14:45:44.506Z] Unsuccessful task run with exit code: 1 completed in 438.243 seconds

[harsh6646]

Hey I'm in Kohilan and Alexei's team and we would like to take this issue.

[La0]

You can make a PR, I'm not exactly sure if this issue is still vaild though.
Ask me for review once you have something ready