Fix storage.py exist_dir logic (flipperdevices#2639)

* Fix storage.py exist_dir logic. This method would return true if the given path existed as either a directory or
a file, which is what the plain exist method is for.

scripts/flipper/storage.py

@@ -323,7 +323,7 @@ def exist_dir(self, path: str):
                 return False
             raise FlipperStorageException.from_error_code(path, error_code)
 
-        return True
+        return response == b"Directory" or response.startswith(b"Storage")
 
     def exist_file(self, path: str):
         """Does file exist on Flipper"""