The method polyhedra for PolyhedralComplex in Polyhedra has an off by 1 in dimension

Given a polyhedral complex, the code
```
polyhedra(1,PC)
```
returns the vertices instead of the edges. For a concrete example,
```
PC = polyhedralComplex hypercube 3;
polyhedra(1,PC)
```
returns
```
{({0}, {}), ({1}, {}), ({2}, {}), ({3}, {}), ({4}, {}), ({5}, {}), ({6}, {}), ({7}, {})}
```
and the cube has 12 edges not 8.

Locate the polyhedra method for PolyhedralComplex and reproduce the hypercube example from the issue. Check how the dimension argument is interpreted, then verify that polyhedra(1,PC) returns the cube's 12 edges rather than its 8 vertices.

Written by the indexing model from the issue text.