fix filetype extension check

main.go

@@ -49,8 +49,11 @@ func isImage(entry os.DirEntry) bool {
 		return false
 	}
 	ext := filepath.Ext(entry.Name())
+	if ext == "" {
+		return false
+	}
 	for _, ft := range validFileTypes {
-		if slices.Contains(ft.TkType.Extensions, ext) {
+		if slices.Contains(ft.MacExtensions, ext[1:]) {
 			return true
 		}
 	}