Fix narrowTypeBySwitchOnDiscriminant function
Fix narrowTypeBySwitchOnDiscriminant function

SaschaNaz/TypeScript,minestarks/TypeScript,kpreisser/TypeScript,weswigham/TypeScript,alexeagle/TypeScript,weswigham/TypeScript,SaschaNaz/TypeScript,alexeagle/TypeScript,basarat/TypeScript,minestarks/TypeScript,Microsoft/TypeScript,kitsonk/TypeScript,SaschaNaz/TypeScript,basarat/TypeScript,donaldpipowitch/TypeScript,microsoft/TypeScript,donaldpipowitch/TypeScript,RyanCavanaugh/TypeScript,donaldpipowitch/TypeScript,nojvek/TypeScript,microsoft/TypeScript,kpreisser/TypeScript,basarat/TypeScript,alexeagle/TypeScript,nojvek/TypeScript,Microsoft/TypeScript,kitsonk/TypeScript,RyanCavanaugh/TypeScript,minestarks/TypeScript,nojvek/TypeScript,Microsoft/TypeScript,donaldpipowitch/TypeScript,kpreisser/TypeScript,RyanCavanaugh/TypeScript,basarat/TypeScript,microsoft/TypeScript,kitsonk/TypeScript,nojvek/TypeScript,SaschaNaz/TypeScript,weswigham/TypeScript