[MRG] Fix AttributeError for encrypted files

[vinayak-mehta]

Fixes #245.

[codecov-io]

Codecov Report

Merging #251 into master will increase coverage by 0.4%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master     #251     +/-   ##
=========================================
+ Coverage   86.98%   87.39%   +0.4%     
=========================================
  Files          13       13             
  Lines        1491     1491             
  Branches      343      343             
=========================================
+ Hits         1297     1303      +6     
+ Misses        137      131      -6     
  Partials       57       57

Impacted Files	Coverage Δ
camelot/handlers.py	90.24% <100%> (ø)	⬆️
camelot/__version__.py	76.47% <100%> (ø)	⬆️
camelot/image_processing.py	94.59% <0%> (+8.1%)	⬆️

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