Fix bug which was reintroduced by previous fix 🤦

[samaloney]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.

Project coverage is 73.50%. Comparing base (2e9bc85) to head (93c524c).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
stixpy/imaging/em.py	0.00%	2 Missing ⚠️
stixpy/calibration/visibility.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #137   +/-   ##
=======================================
  Coverage   73.50%   73.50%           
=======================================
  Files          32       32           
  Lines        2012     2012           
=======================================
  Hits         1479     1479           
  Misses        533      533           

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