Fix T70259: Hair particle point selection if 'use_fade_time' is set

If fade_time is used, particles would be flagged PEK_HIDE (depending on
time settings), but since this is not respected in drawing in 2.8 yet
the user would have no indication of them keys being hidden.
Also doing this for hair doesnt make much sense anyways...

Reviewers: jacqueslucke

Maniphest Tasks: T70259

Differential Revision: https://developer.blender.org/D5901

source/blender/editors/physics/particle_edit.c

@@ -1625,7 +1625,13 @@ void PE_update_object(Depsgraph *depsgraph, Scene *scene, Object *ob, int usefla
   if (pset->flag & PE_AUTO_VELOCITY) {
     update_velocities(edit);
   }
-  PE_hide_keys_time(scene, edit, CFRA);
+
+  /* Only do this for emitter particles because drawing PE_FADE_TIME is not respected in 2.8 yet
+   * and flagging with PEK_HIDE will prevent selection. This might get restored once this is
+   * supported in drawing (but doesnt make much sense for hair anyways). */
+  if (edit->psys->part->type == PART_EMITTER) {
+    PE_hide_keys_time(scene, edit, CFRA);
+  }
 
   /* regenerate path caches */
   psys_cache_edit_paths(depsgraph, scene, ob, edit, CFRA, G.is_rendering);