Unable to start experiment with new account with no former experiments

[KarakoA]

Describe the bug
Unable to start experiment with dvc-cc run -p <EXPERIMENT_NAME> from a new account with no former experiments on execution engine. Crashes due to an IndexError when accessing last experiment id. Stack trace attached.

To Reproduce
Steps to reproduce the behavior:
Follow video tutorial with a new account (with no previous experiments)

Expected behavior
The experiment starts.

Desktop (please complete the following information):

• OS: macOS Mojave 10.14.6

Additional context
Stack Trace:

DVC-CC: Execute jobs.
Switched to branch 'master'
Your branch is up to date with 'origin/master'.
Information: ".dvc/lock" was removed.
Information: delete "cc_execution_file.red.yml
Traceback (most recent call last):
  File "/usr/local/anaconda3/envs/dv3c/bin/dvc-cc", line 8, in <module>
    sys.exit(main())
  File "/usr/local/anaconda3/envs/dv3c/lib/python3.8/site-packages/dvc_cc/main.py", line 69, in main
    cli_modes(SCRIPT_NAME, TITLE, DESCRIPTION, MODES, VERSION)
  File "/usr/local/anaconda3/envs/dv3c/lib/python3.8/site-packages/dvc_cc/cli_modes.py", line 28, in cli_modes
    exit(mode())
  File "/usr/local/anaconda3/envs/dv3c/lib/python3.8/site-packages/dvc_cc/run/main.py", line 708, in main
    cc_id = exec_branch(args.keyring_service)
  File "/usr/local/anaconda3/envs/dv3c/lib/python3.8/site-packages/dvc_cc/run/main.py", line 322, in exec_branch
    last_cc_id = get_last_cc_experimentid(keyring_service)
  File "/usr/local/anaconda3/envs/dv3c/lib/python3.8/site-packages/dvc_cc/run/main.py", line 212, in get_last_cc_experimentid
    return sorted(a,key=lambda x: x['registrationTime'])[-1]['_id']
IndexError: list index out of range

This error is due to GET https://agency.f4.htw-berlin.de/dt/experiments returning an empty list, which causes the Index exception when using [-1] to access its last element.

Will create a PR with simple fix.