Throw error no alias
Thanks for sharing the changes. Closing as wontfix per earlier discussion.

for https://github.com/coleifer/peewee/issues/964.  i know you said no interest, but logging here anyway since i was doing it for my own fork regardless.

the `_join` wound up being unnecessary as far as i can tell.  i couldn't find a path in which it didn't hit the alias_map.

also added a unit test for your concat concern.

changing the unit test because it genned `t4` instead of `t3` i didn't like, but in the end the alias name used doesn't matter, and because if the way the counters are being passed around i'm not sure how fixable it is to keep the `t3`.  (and in my branch all that's gone anyway, so the personal ROI is low to continue debugging)
