Fix T80039: Do not subdivide with Multires is mesh has no faces

This skips the subdivision operation if the mesh has no loops, avoiding
the crash.

Reviewed By: sergey

Maniphest Tasks: T80039

Differential Revision: https://developer.blender.org/D8696

source/blender/blenkernel/intern/multires_reshape.c

@@ -189,6 +189,12 @@ void multiresModifier_subdivide_to_level(struct Object *object,
   }
 
   Mesh *coarse_mesh = object->data;
+  if (coarse_mesh->totloop == 0) {
+    /* If there are no loops in the mesh inplies there is no CD_MDISPS as well. So can early output
+     * from here as there is nothing to subdivide. */
+    return;
+  }
+
   MultiresReshapeContext reshape_context;
 
   /* There was no multires at all, all displacement is at 0. Can simply make sure all mdisps grids