Really fix `autoSelectFirst` interaction with `isSelectable`

This commit fixes a bug that was introduced when I inverted the logic
of `activate`'s second parameter form `shouldNotTrigger` to
`shouldTrigger`. I forgot to invert the logic of a call-point,
causing `autoSelectFirst` to activate and trigger an input-field value
update of the first item in the selection list.

Change-Id: I7c99833ece3f879f1cd836fb3052fd7bfa37e01f
Reviewed-on: https://gerrit.causes.com/19425
Reviewed-by: Tony Wooster <tony.wooster@causes.com>
Tested-by: Tony Wooster <tony.wooster@causes.com>