Add check instead of assert
Add check instead of assert

Reviewed By: jdthomas

Differential Revision: D16032469

fbshipit-source-id: f92dc0722b5792ae6e79fa9b4b272f4064022a48

facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst