Infinite loop if model includes more than one relations to self

backend: `mixer.backend.django`

I get an infinite loop then I try to create objects for model with two ForeignKey fields and relation to self.

For example:
command `mixer.blend(SAPDepartment)` with the model:
```python
class SAPDepartment(models.Model):
sap_name = models.CharField(max_length=150, null=False, blank=False)
sap_id = models.IntegerField()
upper_dep = models.ForeignKey('self', related_name='low_dep', on_delete=models.SET_NULL, null=True)
main_dep = models.ForeignKey('self', related_name='main_department', on_delete=models.SET_NULL, null=True)
```

Start with the Django backend path exercised by mixer.blend(SAPDepartment), using the reported SAPDepartment model with its two self-referential ForeignKey fields. Reproduce the hang and trace the object-generation flow until the repeated self-relations are identified. Done means creating SAPDepartment objects with both relations no longer loops indefinitely.

Written by the indexing model from the issue text.