fix: adjacent_vertices() and incident_edges() are now correct if …

…the `"return.vs.es"` option is `FALSE` (#1606)

R/interface.R

@@ -611,9 +611,9 @@ adjacent_vertices <- function(graph, v,
   on.exit(.Call(R_igraph_finalizer))
 
   res <- .Call(R_igraph_adjacent_vertices, graph, vv, mode)
+  res <- lapply(res, `+`, 1)
 
   if (igraph_opt("return.vs.es")) {
-    res <- lapply(res, `+`, 1)
     res <- lapply(res, unsafe_create_vs, graph = graph, verts = V(graph))
   }