fix: check read permission before entering a folder

src/core/Navigator.py

@@ -1,3 +1,4 @@
+import os
 from pathlib import Path
 from ..items.AItems import AItem
 from ..items.Folder import Folder
@@ -44,24 +45,27 @@ class Navigator:
         else:
             self._cursor.resete()
 
-    def _navigate_to(self, path: Path) -> None:
+    def _navigate_to(self, path: Path) -> bool:
+        if not os.access(path, os.R_OK | os.X_OK):
+            self._error = f"Permission denied: {path}"
+            return False
         self._history.append(path)
+        self._error = None
         self._load()
         self._reset_cursor()
+        return True
 
     def enter(self, item: AItem) -> bool:
         if not item.is_navigable():
             return False
         path = item.point_to if isinstance(item, Symlink) else item.path
-        self._navigate_to(path)
-        return True
+        return self._navigate_to(path)
 
     def up(self) -> bool:
         parent = self._history[-1].parent
         if parent == self._history[-1]:
             return False
-        self._navigate_to(parent)
-        return True
+        return self._navigate_to(parent)
 
     def back(self) -> bool:
         if len(self._history) <= 1: