Fix crash in node when mixing sync/async resolvers (backport of #3706)#3707

IvanGoncharov merged 2 commits into

graphql:16.x.xgraphql/graphql-js:16.x.xfrom

chrskrchr:ck.unhandledRejection2.16.x.xchrskrchr/graphql-js:ck.unhandledRejection2.16.x.xCopy head branch name to clipboard