is_picklable: catch AttributeError (addresses #3771)

[jtamir]

What does this PR do?

Adds an error catch for AttributeError in the utilities.parser.is_picklable function.

Fixes #3771

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[codecov]

Codecov Report

Merging #4508 into master will decrease coverage by 0%.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #4508   +/-   ##
======================================
- Coverage      93%     93%   -0%     
======================================
  Files         116     116           
  Lines        8718    8718           
======================================
- Hits         8086    8075   -11     
- Misses        632     643   +11     

[tchaton]

Great catch !