"undefined field" regression since v0.13.2 with comprehensions and an embedding

[mvdan]

exec cue-v0.13.2 export in.cue
exec cue export in.cue

-- in.cue --
import "strings"

_listBuilder: {
	kind: "kind1"
	_deps: [...]
	_kindJoin: {
		_objs: [...]
		_out: strings.Join([for d in _objs {d.kind}], ",")
	}
	_depKinds: {_kindJoin & {_objs: _deps}}._out
	variable: "{" + _depKinds + "}"
}


output: _
if true {
	_input: [{
		_listBuilder
		_deps: [{_listBuilder}]
	}]

	output: _input[0].variable
}

As of 9461bd2:

> exec cue-v0.13.2 export in.cue
[stdout]
{
    "output": "{kind1}"
}
> exec cue export in.cue
[stderr]
0: undefined field: kind:
    ./in.cue:8:41
[exit status 1]

As reported by @AntoineThebaud via Slack.

[mvdan]

Bisected to commit e44ffe8.