cmd/trace: skip links for buckets with 0 count
cmd/trace: skip links for buckets with 0 count

Change-Id: Ib1c2f7cc8e8f631ed9e74161699332f492d4cb0d
Reviewed-on: https://go-review.googlesource.com/112196
Reviewed-by: Peter Weinberger <dd140fb9530d791057dd8833ea6768ff65fcde71@google.com>

nawawi/go,golang/go,CAFxX/go,josharian/go,nawawi/go,nawawi/go,cloudflare/go,golang/go,CAFxX/go,cloudflare/go,golang/go,golang/go,CAFxX/go,nawawi/go,golang/go,nawawi/go,josharian/go,akutz/go,akutz/go,cloudflare/go,CAFxX/go,golang/go,akutz/go,akutz/go,nawawi/go,CAFxX/go,akutz/go,cloudflare/go,CAFxX/go,CAFxX/go,josharian/go,cloudflare/go,akutz/go,josharian/go,akutz/go,josharian/go,CAFxX/go,josharian/go,nawawi/go,cloudflare/go,golang/go,cloudflare/go,cloudflare/go,golang/go,nawawi/go,josharian/go,akutz/go,josharian/go