cmd/trace: skip links for buckets with 0 count

Change-Id: Ib1c2f7cc8e8f631ed9e74161699332f492d4cb0d
Reviewed-on: https://go-review.googlesource.com/112196Reviewed-by: Peter Weinberger <pjw@google.com>

src/cmd/trace/annotations.go

@@ -861,12 +861,16 @@ func (h *durationHistogram) ToHTML(urlmaker func(min, max time.Duration) string)
 	fmt.Fprintf(w, `<table>`)
 	for i := h.MinBucket; i <= h.MaxBucket; i++ {
 		// Tick label.
+		if h.Buckets[i] > 0 {
 			fmt.Fprintf(w, `<tr><td class="histoTime" align="right"><a href=%s>%s</a></td>`, urlmaker(h.BucketMin(i), h.BucketMin(i+1)), niceDuration(h.BucketMin(i)))
+		} else {
+			fmt.Fprintf(w, `<tr><td class="histoTime" align="right">%s</td>`, niceDuration(h.BucketMin(i)))
+		}
 		// Bucket bar.
 		width := h.Buckets[i] * barWidth / maxCount
-		fmt.Fprintf(w, `<td><div style="width:%dpx;background:blue;top:.6em;position:relative">&nbsp;</div></td>`, width)
+		fmt.Fprintf(w, `<td><div style="width:%dpx;background:blue;position:relative">&nbsp;</div></td>`, width)
 		// Bucket count.
-		fmt.Fprintf(w, `<td align="right"><div style="top:.6em;position:relative">%d</div></td>`, h.Buckets[i])
+		fmt.Fprintf(w, `<td align="right"><div style="position:relative">%d</div></td>`, h.Buckets[i])
 		fmt.Fprintf(w, "</tr>\n")
 
 	}