Fix saving when the cache workspace path is a file

[shreyanshj10]

Pull request

Description

Saving fails permanently with NotADirectoryError: [Errno 20] Not a directory: .../cache/tmp/workspace when the workspace path in the cache directory happens to be a file instead of a directory. cleanup_cache_dir() only catches FileNotFoundError, so shutil.rmtree() raises and every save attempt ends in "An error occurred" until the user deletes that file by hand.

Two changes:

• cleanup_cache_dir() now removes the workspace path with os.remove() when it is a file or a symlink, and keeps using shutil.rmtree() otherwise. The app recovers on its own instead of staying broken.
• create_flatpak_autostart() creates the workspace directory before the cp. This is where the stray file comes from: cp <file> {CACHE}/workspace creates workspace as a file when the directory is not there, and the next create_flatpak_autostart() call would fail on the flatpak-prefs.json write anyway.

Related Issue

• Fixes bug: Can't Save: "An error occurred" #554

Changes Made

• Fixed bug: Describe the bug and how it was fixed.

Screenshots (if applicable)

Not applicable, no visual changes.

Testing

• I have tested my changes via GNOME Builder

I exercised cleanup_cache_dir() directly against three states of the workspace path - missing, an existing directory with content in it, and a plain file - and confirmed that it raises on the third one before the change and leaves an empty directory behind in all three after it.

Checklist

• I have read the contributing guidelines.
• I have performed a self-review of my code.
• I have commented my code where necessary.
• My changes do not introduce any new warnings.

Additional Notes

remove_cache() in gui/window.py and cache_cleanup() in gui/flatpaks_installer_window.py call shutil.rmtree() on the same path behind an os.path.exists() check, so they would hit the same error on a cache that is already in this state. I left them alone to keep this focused on the save path from the issue, but happy to include them if you would like.