Fix #135655: Crash when setting Interpolate Sequences curve

The curve widget in the redo popup would sent an undo push which it
shouldn't really. Since 1bde901bf2 such undo pushes will lead to
clearing of the last operation data, which is exactly what the redo
popup displays.

Buttons in operator redo UIs shouldn't send undo pushes. 179169d6c7
disabled them for the "Adjust Last Operation" panel, but not for this
redo popup. In fact there was other code to disable undo for these
buttons, but 2d2f23de10 put this into a wrongly scoped conditional
branch, so it was only executed on the first full redraw.

We can revert 179169d6c7 too now (confirmed already), but I'll do that
separately and not in the release branch.

Confirmed that the following related issues are all (still) fixed with
this:
- #55348
- #134505
- #135655

Pull Request: https://projects.blender.org/blender/blender/pulls/135730

source/blender/editors/interface/templates/interface_template_operator_property.cc

@@ -177,14 +177,14 @@ static eAutoPropButsReturn template_operator_property_buts_draw_single(
 
   /* set various special settings for buttons */
 
-  /* Only do this if we're not refreshing an existing UI. */
-  if (block->oldblock == nullptr) {
-    const bool is_popup = (block->flag & UI_BLOCK_KEEP_OPEN) != 0;
+  const bool is_popup = (block->flag & UI_BLOCK_KEEP_OPEN) != 0;
 
-    LISTBASE_FOREACH (uiBut *, but, &block->buttons) {
-      /* no undo for buttons for operator redo panels */
-      UI_but_flag_disable(but, UI_BUT_UNDO);
+  LISTBASE_FOREACH (uiBut *, but, &block->buttons) {
+    /* no undo for buttons for operator redo panels */
+    UI_but_flag_disable(but, UI_BUT_UNDO);
 
+    /* Only do this if we're not refreshing an existing UI. */
+    if (block->oldblock == nullptr) {
       /* only for popups, see #36109. */
 
       /* if button is operator's default property, and a text-field, enable focus for it