cmd/cue: fix seems to add duplicated imports if already present

[mvdan]

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

Same as #3405.

Does this issue reproduce with the latest stable release?

Probably; not sure. This relates to the "fix" that @cuematthew is adding now for list arithmetic.

What did you do?

exec cue fix ./...
cmp good/good.cue good/good.cue.fixed

-- good/good.cue --
package good

import "list"

out1: ["foo"] + ["bar"]
out2: list.Repeat(["na"], 10)
-- good/good.cue.fixed --
package good

import "list"

out1: list.Concat([["foo"], ["bar"]])
out2: list.Repeat(["na"], 10)

What did you expect to see?

The testscript should pass.

What did you see instead?

It seems to want to add an import of list6c6973 "list" next to "list", presumably not realising that it's redundant and harmful.

> exec cue fix ./...
> cmp good/good.cue good/good.cue.fixed
diff good/good.cue good/good.cue.fixed
--- good/good.cue
+++ good/good.cue.fixed
@@ -1,9 +1,6 @@
-package p
-
-import (
-	"list"
-	list6c6973 "list"
-)
-
-out1: list6c6973.Concat([["foo"], ["bar"]])
+package good
+
+import "list"
+
+out1: list.Concat([["foo"], ["bar"]])
 out2: list.Repeat(["na"], 10)

FAIL: repro-cmd.txtar:2: good/good.cue and good/good.cue.fixed differ

Again, found when trying to use cue fix ./... on Unity projects.