alias function partly broken in peewee 3.9.4 and 3.9.5
Thanks, I've been able to replicate this and am working on a fix. Fixed, pushing a new release 3.9.6 See also #1914 Sorry to be bugging you again, but will you be pushing the new release to pypi? I thought I had, 3.9.6? https://github.com/coleifer/peewee/releases/tag/3.9.6 Oh, guess not, done. Great, thank you!
I just upgraded from peewee 3.9.3 to 3.9.5 and suddenly I am getting the following error:

```  File "/home/anne/projects/recapi/recapi/views/recipe_data.py", line 39, in get_recipe_data
    User, pw.JOIN.LEFT_OUTER, on=(User.id == recipemodel.Recipe.created_by).alias("a")
  File "/home/anne/projects/recapi/venv/lib/python3.7/site-packages/peewee.py", line 698, in inner
    method(clone, *args, **kwargs)
  File "/home/anne/projects/recapi/venv/lib/python3.7/site-packages/peewee.py", line 6603, in join
    on, attr, constructor = self._normalize_join(src, dest, on, attr)
  File "/home/anne/projects/recapi/venv/lib/python3.7/site-packages/peewee.py", line 6534, in _normalize_join
    attr == fk_field.object_id_name and not is_backref:
AttributeError: 'AutoField' object has no attribute 'object_id_name'
```

The same error occurs in peewee 3.9.4 but everything is running fine in 3.9.3. The code piece that breaks looks like this:

```Changed = User.alias()
recipes = recipemodel.Recipe.select(
    recipemodel.Recipe, User, Changed, pw.fn.group_concat(tagmodel.Tag.tagname).alias("taglist")
).where(
    recipemodel.Recipe.published == published
).join(
    User, pw.JOIN.LEFT_OUTER, on=(User.id == recipemodel.Recipe.created_by).alias("a")
).switch(
    recipemodel.Recipe
).join(
    Changed, pw.JOIN.LEFT_OUTER, on=(Changed.id == recipemodel.Recipe.changed_by).alias("b")
).switch(
    recipemodel.Recipe
).join(
    tagmodel.RecipeTags, pw.JOIN.LEFT_OUTER, on=(tagmodel.RecipeTags.recipeID == recipemodel.Recipe.id)
).join(
    tagmodel.Tag, pw.JOIN.LEFT_OUTER, on=(tagmodel.Tag.id == tagmodel.RecipeTags.tagID)
).group_by(recipemodel.Recipe.id)
```

It's the `.alias("a")` and `.alias("b")` bits that seem to be causing the trouble.

Please let me know if there is any relevant information lacking from this bug report.