Objects: make evaluated data runtime storage usable for types other than mesh

This is in preparation of new object types. This only changes mesh_eval, we
may do the same for mesh_deform_eval and other areas in the future if there is
a need for it.

This previously caused a bug in T74283, that should be fixed now.

Differential Revision: https://developer.blender.org/D6695

source/blender/blenkernel/intern/modifier.c

@@ -1019,7 +1019,7 @@ Mesh *BKE_modifier_get_evaluated_mesh_from_evaluated_object(Object *ob_eval,
   if (me == NULL) {
     me = (get_cage_mesh && ob_eval->runtime.mesh_deform_eval != NULL) ?
              ob_eval->runtime.mesh_deform_eval :
-             ob_eval->runtime.mesh_eval;
+             BKE_object_get_evaluated_mesh(ob_eval);
   }
 
   return me;