Fixes an error when no config file present (assume default config) + tests

[athril]

• fixes #40
• updates to client.py and test_client.py when no config/incorrect config provided

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 100.00%. Comparing base (e39a579) to head (c71a2c0). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #41 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 9 9 Lines 446 450 +4 ========================================= + Hits 446 450 +4 ``` | [Flag](https://app.codecov.io/gh/nih-sparc/sparc.client/pull/41/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nih-sparc) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/nih-sparc/sparc.client/pull/41/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nih-sparc) | `100.00% <100.00%> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nih-sparc#carryforward-flags-in-the-pull-request-comment) to find out more.

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