validateProcessSpec: prevent SEGV when config is valid json, but invalid.
validateProcessSpec: prevent SEGV when config is valid json, but invalid.

Signed-off-by: John Hwang <e0e4e82459f9b612655ef54f67653c842bf3b961@gmail.com>

kolyshkin/runc,mikebrow/runc,rhatdan/runc,estesp/runc,estesp/runc,opencontainers/runc,opencontainers/runc,xiaochenshen/runc,opencontainers/runc,rhatdan/runc,kolyshkin/runc,dqminh/runc,dqminh/runc,dqminh/runc,xiaochenshen/runc,dqminh/runc,rhatdan/runc,xiaochenshen/runc,estesp/runc,kolyshkin/runc,opencontainers/runc,mikebrow/runc,rhatdan/runc,kolyshkin/runc,mikebrow/runc