test: test issue 7884 (already fixed)
test: test issue 7884 (already fixed)

I don't know when the bug was fixed, but empirically it was.
Make sure it stays fixed by adding a test.

Fixes issue 7884.

LGTM=adg
R=golang-codereviews, adg
CC=golang-codereviews
https://codereview.appspot.com/93500043

d0f/go-zh,bryanxu/go-zh,webfd/go-zh,bryanxu/go-zh,bryanxu/go-zh,bryanxu/go-zh,sanjosh/sanjos100-tipc,sanjosh/sanjos100-tipc,d0f/go-zh,d0f/go-zh,webfd/go-zh,d0f/go-zh,sanjosh/sanjos100-tipc,sanjosh/sanjos100-tipc,webfd/go-zh,sanjosh/sanjos100-tipc,webfd/go-zh,bryanxu/go-zh,webfd/go-zh,bryanxu/go-zh,d0f/go-zh,sanjosh/sanjos100-tipc,d0f/go-zh,sanjosh/sanjos100-tipc,sanjosh/sanjos100-tipc,bryanxu/go-zh,webfd/go-zh,bryanxu/go-zh,d0f/go-zh,webfd/go-zh,d0f/go-zh,webfd/go-zh