subgraph_isomorphism on filtered graph / GraphView => segfaults

Dear Tiago,

Thank you for your great work on this very useful library! I have
played with it for a project over the last few days, and today I have
discovered a real roadblock: subgraph_isomorphism seems to segfault (at
least very often, have not found any pattern yet) when searching on a
graph with filtered vertices (or the equivalent GraphView) --- this has
never occurred to me for an unfiltered graph. Here is a minimal

Hi Ingo,