cmd/trace: handle invalid goid para in /trace
cmd/trace: handle invalid goid para in /trace

Change-Id: I1cb7c8b70a5ae16386f6abb577c23d821f7ff7f0
Reviewed-on: https://go-review.googlesource.com/112197
Reviewed-by: Peter Weinberger <dd140fb9530d791057dd8833ea6768ff65fcde71@google.com>
Run-TryBot: Hyang-Ah Hana Kim <d7e82c3c07f92613bcbf9a1e88f6b96c13caa3b0@gmail.com>

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