(v6.x backport) os,vm: fix segfaults and CHECK failure#13871

tniessen wants to merge 1 commit intonodejs:v6.x-stagingnodejs/node:v6.x-stagingfrom

tniessen:backport-12371-to-v6.xtniessen/node:backport-12371-to-v6.xCopy head branch name to clipboard