liblink: fix precedence bug in pcdata comparison
liblink: fix precedence bug in pcdata comparison

As written, the ! applies before the &1.
This would crash writing out missing pcdata tables
if we ever used non-contiguous IDs in a function.
We don't, but fix anyway.

LGTM=iant, minux
R=minux, iant
CC=golang-codereviews
https://codereview.appspot.com/117810047

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