Fix #113760: Knife Tool: wrong red point after undo

After confirming a cut, the tool goes into `MODE_IDLE`.
In `knifetool_undo`, the `KnifePosData` `prev` (drawn as the "red point"
in question in `knifetool_draw`) was only set to the `KnifeUndoFrame`
pos when we are in `MODE_DRAGGING` though -- this is now changed to also
be done for `MODE_IDLE`.

NOTE: it might be questionable to even draw this bigger red dot once a
cut is confirmed (will attach another small diff to the PR that does
this)

Pull Request: https://projects.blender.org/blender/blender/pulls/133430

source/blender/editors/mesh/editmesh_knife.cc

@@ -3862,7 +3862,7 @@ static void knifetool_undo(KnifeTool_OpData *kcd)
     }
   }
 
-  if (kcd->mode == MODE_DRAGGING) {
+  if (ELEM(kcd->mode, MODE_DRAGGING, MODE_IDLE)) {
     /* Restore kcd->prev. */
     kcd->prev = undo->pos;
   }