fix: prevent IntegrityError when deleting user account

[Simon99]

Summary

Fixes the IntegrityError that occurs when a user deletes their account.

Problem

When a user deletes their account, Django cascades the deletion to related objects (WorkoutLog, WorkoutSession). The post_delete signal handlers try to recalculate user statistics, but the user no longer exists at that point, causing an IntegrityError:

IntegrityError: insert or update on table "trophies_userstatistics" 
violates foreign key constraint "trophies_userstatistics_user_id_0de72480_fk_auth_user_id"
DETAIL: Key (user_id)=(....) is not present in table "auth_user".

Solution

Added User.DoesNotExist checks in both delete signal handlers before attempting to update statistics:

• workout_log_deleted() - checks if user exists before recalculating
• workout_session_deleted() - checks if user exists before recalculating

If the user has been deleted, we skip the statistics update and log a debug message.

Changes

• Modified wger/trophies/signals.py
  • Added User existence check in workout_log_deleted
  • Added User existence check in workout_session_deleted
  • Added debug logging when skipping updates for deleted users

Testing

The fix handles the race condition where:

1. User deletion triggers cascade deletion of logs/sessions
2. Delete signals fire for each deleted object
3. Signal handlers check if user still exists
4. If user is deleted, skip statistics update gracefully

Fixes

Fixes #2232

[rolandgeider]

hey thanks for the PR!

however somebody else had already started working on this in #2233 (it seems they started half an hour before you) so I'll close this PR, sorry