Fix ambiguous conversion
Fix ambiguous conversion

Summary: Mollify some versions of GCC, hopefully.

Reviewed By: Feng23

Differential Revision: D19700553

fbshipit-source-id: 82b310142021dc4ee934bf8ffa9fe18e4c317d7d

facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex