Fix #111073: Crash when F3 is pressed

Initializing a string whit `nullptr` causes undefined behavior.

Pull Request: https://projects.blender.org/blender/blender/pulls/111075

source/blender/editors/interface/interface_template_search_menu.cc

@@ -168,7 +168,7 @@ static bool menu_items_from_ui_create_item_from_button(MenuSearch_Data *data,
   MenuSearch_Item *item = nullptr;
 
   /* Use override if the name is empty, this can happen with popovers. */
-  std::string drawstr_override = nullptr;
+  std::string drawstr_override;
   const char *drawstr_sep = (but->flag & UI_BUT_HAS_SEP_CHAR) ?
                                 strrchr(but->drawstr, UI_SEP_CHAR) :
                                 nullptr;