prs2net has erroneous message for positive labels used in a distributed shared gate network

[nbingham1]

Describe the bug
unexpected error message for shared gate network

To Reproduce
Steps to reproduce the behavior:

1. Use the ACT source included below.
2. prs2net -p'test<>' temp.act
3. produces an error message FATAL: @-expression with unknown label 'x'

ACT source
temp.act

defproc test() {
  bool a, b, c;
  prs {
    ~a -> @x+
  }

  (;i:2:
    prs {
      @x & ~b -> c+
    }
  )
}

test t;

Expected behavior
expected netlist output

Computer setup (please complete the following information):
g++ (Ubuntu 10.2.0-13ubuntu1) 10.2.0
LSB Version: core-11.1.0ubuntu2-noarch:security-11.1.0ubuntu2-noarch
Distributor ID: Ubuntu
Description: Ubuntu 20.10
Release: 20.10
Codename: groovy

Additional context
inverting the sense of the label works properly

[rmanohar]

Thanks. I pushed a fix.

[nbingham1]

Yep, it works