Fix 'x instanceof ctor' where type of ctor is Function

Author: ahejlsberg

src/compiler/checker.ts

@@ -15351,24 +15351,13 @@ namespace ts {
                 }
 
                 if (!targetType) {
-                    // Target type is type of construct signature
-                    let constructSignatures: ReadonlyArray<Signature> | undefined;
-                    if (getObjectFlags(rightType) & ObjectFlags.Interface) {
-                        constructSignatures = resolveDeclaredMembers(<InterfaceType>rightType).declaredConstructSignatures;
-                    }
-                    else if (getObjectFlags(rightType) & ObjectFlags.Anonymous) {
-                        constructSignatures = getSignaturesOfType(rightType, SignatureKind.Construct);
-                    }
-                    if (constructSignatures && constructSignatures.length) {
-                        targetType = getUnionType(map(constructSignatures, signature => getReturnTypeOfSignature(getErasedSignature(signature))));
-                    }
+                    const constructSignatures = getSignaturesOfType(rightType, SignatureKind.Construct);
+                    targetType = constructSignatures && constructSignatures.length ?
+                        getUnionType(map(constructSignatures, signature => getReturnTypeOfSignature(getErasedSignature(signature)))) :
+                        emptyObjectType;
                 }
 
-                if (targetType) {
-                    return getNarrowedType(type, targetType, assumeTrue, isTypeDerivedFrom);
-                }
-
-                return type;
+                return getNarrowedType(type, targetType, assumeTrue, isTypeDerivedFrom);
             }
 
             function getNarrowedType(type: Type, candidate: Type, assumeTrue: boolean, isRelated: (source: Type, target: Type) => boolean) {