UnboundLocalError after copying files on the Boot tab.

[Cubic PPA]

An UnboundLocalError occurs after copying files on the Boot tab, navigating away from the Options page, and then navigating back to the Options page, Boot tab.

Steps to reproduce:
1. On the boot tab, copy a directory structure containing files.
   For example, copy a directory containing files and directories into boot/grub/x86_64-efi
2. Click the Back button to navigate away from the Options page.
3. Click the Next button to navigate to the Options page.
4. The following error occurs:

    Traceback (most recent call last):
      File "/usr/share/cubic/cubic/utilities/files_tab.py", line 1009, in _search_and_replace_in_files
        self.files_tree.search_and_replace_in_file(file_path, search_replace_tuples)
      File "/usr/share/cubic/cubic/utilities/files_tree.py", line 645, in search_and_replace_in_file
        tree_model.set_value(tree_iter, FILE_ICON, file_icon)
    UnboundLocalError: local variable 'tree_model' referenced before assignment

[Cubic PPA (cubic-wizard)]

Fix released in version 2021.03-48.

[Cubic PPA (cubic-wizard)]

CORRECTION: Fix released in version 2021.04-48.