Nyall Dawson c6613593c7 Don't loop through all selected features multiple times (once per
field) when the attribute form is opened.

This is incredibly expensive, yet only required in a very very small
corner case (field is from a joined layer without the upsert on edit
capabilities).

Refine logic to avoid the scan wherever we can.

Fixes #41366
Fixes #36863
2021-02-09 10:24:45 +10:00
..