[postgres] Type name for custom enum is not always attached to TypeInfo

[Celti]

This leads to errors like "mismatched types; Rust type `eris::db::ActivityKind` (as SQL type activity_kind) is not compatible with SQL type " with the following types.

Minimal reproduction: https://gist.github.com/Celti/7a9bc788ace5620825096961ce88ab70
This is with sqlx 0.3.3 and postgres 12.2.

[mehcode]

Thanks for the report and the reproduction @Celti

Can you check master to see if it works for you?

[Celti]

Works like a charm! Thanks!