pkg/jsonmessage: fix "Multiplication of durations" (durationcheck)

pkg/jsonmessage/jsonmessage.go:111:10: Multiplication of durations: `(left / time.Second) * time.Second` (durationcheck)
            left = (left / time.Second) * time.Second
                   ^

This code was rounding down time remaining to the nearest second;

- Use go's time.Duration.Round() instead
- Make the calculation conditional, as it was only used if there's enough
  space available to print
- Move the declaration of the timeLeftBox var closer to where used.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

pkg/jsonmessage/jsonmessage.go

@@ -53,10 +53,9 @@ type JSONProgress struct {
 
 func (p *JSONProgress) String() string {
 	var (
-		width       = p.width()
-		pbBox       string
-		numbersBox  string
-		timeLeftBox string
+		width      = p.width()
+		pbBox      string
+		numbersBox string
 	)
 	if p.Current <= 0 && p.Total <= 0 {
 		return ""
@@ -104,14 +103,14 @@ func (p *JSONProgress) String() string {
 		}
 	}
 
-	if p.Current > 0 && p.Start > 0 && percentage < 50 {
-		fromStart := p.now().Sub(time.Unix(p.Start, 0))
-		perEntry := fromStart / time.Duration(p.Current)
-		left := time.Duration(p.Total-p.Current) * perEntry
-		left = (left / time.Second) * time.Second
-
-		if width > 50 {
-			timeLeftBox = " " + left.String()
+	// Show approximation of remaining time if there's enough width.
+	var timeLeftBox string
+	if width > 50 {
+		if p.Current > 0 && p.Start > 0 && percentage < 50 {
+			fromStart := p.now().Sub(time.Unix(p.Start, 0))
+			perEntry := fromStart / time.Duration(p.Current)
+			left := time.Duration(p.Total-p.Current) * perEntry
+			timeLeftBox = " " + left.Round(time.Second).String()
 		}
 	}
 	return pbBox + numbersBox + timeLeftBox