Foundation: avoid unnecessary disk IO on windows file enumeration

Prefer to use the `hasDirectoryPath` ivar on the URL which should be
properly populated when populating the stack.  The one special case is
when we first initialise the enumerator, where we can assume that we are
given a directory path.

Author: compnerd

Sources/Foundation/FileManager+Win32.swift

@@ -930,14 +930,14 @@ extension FileManager {
         var _errorHandler : ((URL, Error) -> Bool)?
         var _stack: [URL]
         var _lastReturned: URL
-        var _rootDepth : Int
+        var _rootDepth: Int
 
         init(url: URL, options: FileManager.DirectoryEnumerationOptions, errorHandler: (/* @escaping */ (URL, Error) -> Bool)?) {
             _options = options
             _errorHandler = errorHandler
             _stack = []
             _rootDepth = url.pathComponents.count
-            _lastReturned = url
+            _lastReturned = URL(fileURLWithPath: url.path, isDirectory: true)
         }
 
         override func nextObject() -> Any? {
@@ -959,16 +959,7 @@ extension FileManager {
             }
 
             // If we most recently returned a directory, decend into it
-            guard let attrs = try? FileManager.default.windowsFileAttributes(atPath: _lastReturned.path) else {
-                guard let handler = _errorHandler,
-                    handler(_lastReturned, _NSErrorWithWindowsError(GetLastError(), reading: true, paths: [_lastReturned.path]))
-                else { return nil }
-                return firstValidItem()
-            }
-
-            let isDir = attrs.dwFileAttributes & DWORD(FILE_ATTRIBUTE_DIRECTORY) == DWORD(FILE_ATTRIBUTE_DIRECTORY) &&
-                attrs.dwFileAttributes & DWORD(FILE_ATTRIBUTE_REPARSE_POINT) == 0
-            if isDir && (level == 0 || !_options.contains(.skipsSubdirectoryDescendants)) {
+            if _lastReturned.hasDirectoryPath && (level == 0 || !_options.contains(.skipsSubdirectoryDescendants)) {
                 var ffd = WIN32_FIND_DATAW()
                 let capacity = MemoryLayout.size(ofValue: ffd.cFileName)