cue/errors: make wrapped.Path faster by bypassing unnecessary reflection

This makes one of our cue cmd runs noticeably faster, from ~52s to ~36s.

Change-Id: I735875bfcd8b08f329a59a903d4c7c1ae195f269
Signed-off-by: Maximilian Gaß <[email protected]>
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1198494
TryBot-Result: CUEcueckoo <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>
Reviewed-by: Daniel Martí <[email protected]>

cue/errors/errors.go

@@ -223,7 +223,7 @@ func (e *wrapped) Msg() (format string, args []interface{}) {
 }
 
 func (e *wrapped) Path() []string {
-	if p := Path(e.main); p != nil {
+	if p := e.main.Path(); p != nil {
 		return p
 	}
 	return Path(e.wrap)