Fix a bug on windows when isHiddenFile returns an error

ishidden_windows.go

@@ -3,17 +3,32 @@
 package watcher
 
 import (
+	"os"
 	"syscall"
 )
 
 func isHiddenFile(path string) (bool, error) {
 	pointer, err := syscall.UTF16PtrFromString(path)
 	if err != nil {
+		if os.IsNotExist(err) {
+			err = &os.PathError{
+				Op:   "isHidden",
+				Path: path,
+				Err:  err,
+			}
+		}
 		return false, err
 	}
 
 	attributes, err := syscall.GetFileAttributes(pointer)
 	if err != nil {
+		if os.IsNotExist(err) {
+			err = &os.PathError{
+				Op:   "isHidden",
+				Path: path,
+				Err:  err,
+			}
+		}
 		return false, err
 	}
 

ishidden_windows_test.go

@@ -0,0 +1,19 @@
+// +build windows
+
+package watcher
+
+import (
+	"os"
+	"testing"
+)
+
+func TestIsHiddenFileReturnsPathError(t *testing.T) {
+	_, err := isHiddenFile("./qqdkqdsdmlqdsd.nop")
+	if err == nil {
+		t.Fatal("isHidden should have returned an error")
+	}
+
+	if _, ok := err.(*os.PathError); !ok {
+		t.Fatal("Error is not a PathError")
+	}
+}