fix: isomorphisms() and subgraph_isomorphisims(method = "vf2") work again, regression introduced in 2.0.0

[krlmlr]

Closes #1218.

@szhorvat: With this, I'm seeing:

motif <- igraph::make_empty_graph(directed = FALSE) +
  igraph::vertices("D1", "D2", type = c("type1", "type1")) +
  igraph::edges("D1", "D2", type = c("type2"))
igraph::subgraph_isomorphisms(
  target = motif, pattern = motif, method = "vf2",
  vertex.color1 = 2, vertex.color2 = 1
)
#> Error in graph.get.subisomorphisms.vf2(target, pattern, ...): At vendor/cigraph/src/isomorphism/vf2.c:1089 : Invalid vertex color vector length, Invalid value

^{Created on 2024-02-08 with reprex v2.1.0}

Do you expect this error?

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[szhorvat]

Yes, it is expected. The colour vector must contain one entry for each vertex. So if you have two vertices, you need a colour vector of length 2.

[krlmlr]

According to your remark in the issue, this fix isn't optimal, we should be using INTEGER() instead of REAL() here? Would you like to propose a better fix?

[szhorvat]

Can I push to this branch?

[szhorvat]

I'm sorry, I misspoke. This is fine. Please merge this. I'll submit a separate improvement for the LAD function later. Don't wait for that with the new bugfix release.

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This pull request can't be queued because it's currently a draft.