Merge pull request ipfs/go-ipfs-files#39 from ipfs/masih/fix-win-test…

…-fail

Fix test failure on Windows caused by nil `sys` in mock `FileInfo`

This commit was moved from ipfs/go-ipfs-files@ac44de8

files/is_hidden_windows.go

@@ -19,7 +19,11 @@ func isHidden(fi os.FileInfo) bool {
 		return true
 	}
 
-	wi, ok := fi.Sys().(*windows.Win32FileAttributeData)
+	sys := fi.Sys()
+	if sys == nil {
+		return false
+	}
+	wi, ok := sys.(*windows.Win32FileAttributeData)
 	if !ok {
 		return false
 	}