Hierarchical port spacing not correct for compound nodes

[le-cds]

For compound nodes laid out with ELK Layered, the minimum spacing between adjacent hierarchical ports may not be correct since the usual node-node spacing is probably applied to them.

[soerendomroes]

This is probably the same issue described in #766 and will hopefully be fixed. The issue was that ports are assigned a size of 1 instead of 0.