non-zero initialization of ICON mesh index mapping (consistency check).

Author: Florian Prill

graphs/src/anemoi/graphs/generate/icon_mesh.py

@@ -148,7 +148,7 @@ def _restrict_multi_mesh_edges_and_cells(
         """Creates a new mesh with only the vertices at the desired level."""
         vertex_mask = self.reflvl_vertex <= self.max_level
         num_vertices = vertex_mask.shape[0]
-        vertex_glb2loc = np.zeros(num_vertices, dtype=int)
+        vertex_glb2loc = np.full(num_vertices, -1, dtype=int)
         vertex_glb2loc[vertex_mask] = np.arange(vertex_mask.sum())
         return (
             [vertex_glb2loc[vertices] for vertices in edge_vertices[: self.max_level + 1]],