RecursionError in __setattr__ when the tenant_field is not loaded initially.

The case: Run query with Django's `only()` and did not include the `tenant_field` in only fields, something like below:
```
bot= BotUser.objects.only("id").first()
django.core.serializers.serialize("json",[bot])
```
We will get the RecursionError: `__setattr__` > `refresh_from_db` > `__setattr__` > `refresh_from_db` > ........

The error details are as follows:
`__setattr__`= django_multitenant.__setattr__

1. When we try to access the field not included in only (e.g. name of BotUser), `__setattr__` triggered to set result from DB
2. When `__setattr__` triggered, trigger `is_val_equal_to_tenant` but `tenant_value` not set/fetched yet
3. `__setattr__` triggered to set `tenant_value` result from DB
4. When `__setattr__` triggered, `tenant_value` not able to set, because of `tenant_value` not set/fetched yet (step 2)

**I think the checking should not be run when `tenant_field` not set yet**

---

**Possible fix:**

```Python
def __setattr__(self, attrname, val):
def is_val_equal_to_tenant(val):
if self.tenant_field not in self.__dict__:
return True #Skip check when `tenant_field` not set yet
return......# remain unchanged
.....# remain unchanged
```

---

For quick fix, just ensuring the `tenant_field` always set before accessing any fields