Fix particle-edit crash on undo/redo

Undo/redo was crashing & asserting.

There ware two bugs:

- Entering particle system edit-mode requires an evaluated depsgraph.

- The active object could get out of sync when undo/redo
  moves between different modes.

The new test 'view3d_mesh_particle_edit_mode_simple'
in `tests/ui_simulate/test_undo.py` exposes both issues.

1 files changed, 3 insertions, 0 deletions

diff --git a/source/blender/editors/physics/particle_edit.c b/source/blender/editors/physics/particle_edit.c
index ec3eb9c6a3a..d0ebac82c90 100644
--- a/source/blender/editors/physics/particle_edit.c
+++ b/source/blender/editors/physics/particle_edit.c
@@ -5395,6 +5395,9 @@ static void free_all_psys_edit(Object *object)
 
 void ED_object_particle_edit_mode_enter_ex(Depsgraph *depsgraph, Scene *scene, Object *ob)
 {
+  /* Needed so #ParticleSystemModifierData.mesh_final is set. */
+  BKE_scene_graph_evaluated_ensure(depsgraph, G_MAIN);
+
   PTCacheEdit *edit;
 
   ob->mode |= OB_MODE_PARTICLE_EDIT;