Cue fmt drags comments into import block

[cueckoo]

Originally opened by @ah-edg in cuelang/cue#720

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

$ cue version
cue version 0.3.0-beta.3 linux/amd64

Does this issue reproduce with the latest release?

yes

What did you do?

Run cue fmt on this input:

import "encoding/base64"

// comment

#A: {}

What did you expect to see?

no change

What did you see instead?

import ( "encoding/base64"

	// comment
)

#A: {}

[rudifa]

This is same as cmd/fmt: single import and comment combined #1447.

The newline after the comment triggers the bug, as the comment gets associated with the previous import line, then the comment is misplaced into the import block.

In the absence of a newline between the comment and the code following it there is no problem, and the fmt output is same as input.