fix bug where image was 64-bit in case where no extraction is needed

[kosack]

No description provided.

[kosack]

we're missing a test for telescopes with no extraction needed. Though I guess the tool test will fail in this case.

[codecov]

Codecov Report

Merging #1339 into master will decrease coverage by 0.00%.
The diff coverage is 90.15%.

@@            Coverage Diff             @@
##           master    #1339      +/-   ##
==========================================
- Coverage   91.05%   91.05%   -0.01%     
==========================================
  Files         179      179              
  Lines       12192    12205      +13     
==========================================
+ Hits        11102    11113      +11     
- Misses       1090     1092       +2     

Impacted Files	Coverage Δ
ctapipe/calib/camera/flatfield.py	95.04% <ø> (ø)
ctapipe/core/container.py	88.35% <ø> (ø)
ctapipe/image/extractor.py	86.00% <0.00%> (-0.87%)	⬇️
ctapipe/image/hillas.py	98.07% <90.90%> (ø)
ctapipe/io/tests/test_hdf5.py	97.79% <94.73%> (ø)
ctapipe/calib/camera/calibrator.py	100.00% <100.00%> (ø)
ctapipe/calib/camera/pedestals.py	94.94% <100.00%> (ø)
ctapipe/calib/camera/tests/test_calibrator.py	100.00% <100.00%> (ø)
ctapipe/containers.py	100.00% <100.00%> (ø)
ctapipe/core/tests/test_traits.py	100.00% <100.00%> (ø)
... and 19 more

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