Fix RecursionError for duplicate files

[dvdl16]

Fixes #132

1. Guard associate_files() behind a flag so a save triggered from within association does not re-run association:

def validate(self):
    # guard against recursion: associate_files() can save another File, re-entering validate
    if not self.flags.associating_files:
        self.associate_files()
    ...

2. Set the flag before saving the duplicate in associate_files():

existing_file.flags.associating_files = True
existing_file.save()

3. Avoid duplicate file_association child rows - only append the association if the same link_doctype / link_name isn't already present:

already_linked = any(
   assoc.link_doctype == attached_to_doctype and assoc.link_name == attached_to_name
   for assoc in existing_file.file_association
)
if not already_linked:
   existing_file.append(
       "file_association",
       add_child_file_association(attached_to_doctype, attached_to_name),
   )

This breaks the recursion while still performing the intended one-pass association, and prevents redundant association rows from accumulating.

[dvdl16]

@agritheory Thank you for this app! As I'm not a collaborator, I don't think the failing actions have access to the necessary env vars. Let me know how you'd like me to proceed

[lauty95]

Hey @dvdl16 thanks for this fix!

The tests pass locally, but I noticed that this PR doesn't add regression tests for this scenario.

Could you add a couple of tests for this?
Two tests that would help:

• Create two File docs with identical content_hash (via db_insert(), bypassing the merge-on-insert), then .save() one of them and assert it completes without RecursionError.
• Call associate_files() twice with the same link_doctype/link_name and assert file_association doesn't grow a duplicate row (covers the new already_linked guard).

To run the suite locally:

Activate the bench virtualenv: source env/bin/activate
Make sure sites/currentsite.txt contains your site name
Run: pytest --disable-warnings -s from apps/cloud_storage

[dvdl16]

Thank you @lauty95! Will do and revert back