Fix minor issue

Author: ahejlsberg

src/compiler/checker.ts

@@ -6444,7 +6444,8 @@ namespace ts {
                 for (const declaration of symbol.declarations) {
                     if (declaration.kind === SyntaxKind.EnumDeclaration) {
                         for (const member of (<EnumDeclaration>declaration).members) {
-                            const memberType = getFreshTypeOfLiteralType(getLiteralType(getEnumMemberValue(member) || 0, enumCount, getSymbolOfNode(member)));
+                            const value = getEnumMemberValue(member);
+                            const memberType = getFreshTypeOfLiteralType(getLiteralType(value !== undefined ? value : 0, enumCount, getSymbolOfNode(member)));
                             getSymbolLinks(getSymbolOfNode(member)).declaredType = memberType;
                             memberTypeList.push(getRegularTypeOfLiteralType(memberType));
                         }