Fix nEdges float --> int in graph files

[xylar]

Before this fix, we were seeing culled_graph.info files like:

7435 21369.0
8 3 2
1 7 9 8
...

The number of edges was being converted to a float because of a non-integer division by 2.

Checklist

• Document (in a comment titled Testing in this PR) any testing that was used to verify the changes

[xylar]

Testing

I ran the QUwISC240 mesh test case after cherry-picking these 2 commits onto #668. I now see:

7435 21369
8 3 2
1 7 9 8
8 10 4 1
...

as expected.