Fixes #12423 - Additional select columns are removed when using includes

Hmm.

@senny @sgrif if we get back a 705 ("unknown"), should we just treat it as a string, rather than blow up? That seems to be how psql, for example, behaves.. and it doesn't seem unreasonable: about the only way to actually see that type is from a bare quoted literal (AFAIK?), and absent any hint to the contrary, it doesn't seem a big leap.