Change what DensePoseResultExtractor returns in case of error
Change what DensePoseResultExtractor returns in case of error

Summary: Change what DensePoseResultExtractor returns in case of error

Reviewed By: patricklabatut

Differential Revision: D24731175

fbshipit-source-id: 65e47d9f58227b5aaec671333b722fb4d27d44fe

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