Skip the test when there is no .gosymtab section in the executable
rather than crashing.

Change-Id: Ieb3df07e307f50c33cdafab38f9b5d1ac0e55c04
Reviewed-on: https://go-review.googlesource.com/5110Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Michael Hudson-Doyle <michael.hudson@canonical.com>