FIX: Gracefully warn when no motion components are found

[jczimm]

Changes proposed in this pull request

Fixes #82

Documentation that should be reviewed

N/A

[effigies]

LGTM. Thanks!

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 30.59%. Comparing base (8cba0aa) to head (5a7ffd9).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/fmripost_aroma/interfaces/confounds.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #83   +/-   ##
=======================================
  Coverage   30.59%   30.59%           
=======================================
  Files          26       26           
  Lines        2363     2363           
  Branches      286      286           
=======================================
  Hits          723      723           
  Misses       1617     1617           
  Partials       23       23           

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