internal/core/adt: dynamic fields not properly resolve with default values

[mpvl]

What version of CUE are you using (cue version)?

near-tip:
cue version v0.0.0-20220812162136-7ad3777f9942

   -compiler gc
 CGO_ENABLED 1
      GOARCH amd64
        GOOS darwin
     GOAMD64 v1
         vcs git
vcs.revision 7ad3777f9942877b60cd9036c84dc9f6a0c0a951
    vcs.time 2022-08-12T16:21:36Z
vcs.modified true

Does this issue reproduce with the latest release?

Yes

What did you do?

cue eval -

b: {
        c: *"d" | string
        (c): 2
}

What did you expect to see?

success

What did you see instead?

An unresolved dynamic fields

b: {
    c:   *"d" | string
    (c): 2
}

Discovered when investigating #1795