fix(menu): preview not updated after returning to prev menu

Bug:    After returning from a sub-menu to its previous menu, the
        preview of the symbol under cursor in the previous menu
        is not started.
Fix:     The issue stems from the conditional check in
         `dropbar_menu_t:preview_symbol_at()`. It compares the component
         to be previewed with `self.symbol_previewed` and returns early
         if they match, aiming to reduce unnecessary calls to
         `dropbar_symbol_t:preview()`. However, this approach becomes
         problematic when returning from sub-menus to their previous
         menus, as the `symbol_previewed` of the previous menu
         consistently matches the symbol under the cursor, preventing
         the symbol's preview from starting. Removing the check fixes
         the issue.

lua/dropbar/menu.lua

@@ -730,7 +730,7 @@ function dropbar_menu_t:preview_symbol_at(pos, look_ahead)
     return
   end
   local component = self:get_component_at(pos, look_ahead)
-  if not component or component == self.symbol_previewed then
+  if not component then
     return
   end
   component:preview(self.symbol_previewed and self.symbol_previewed.view)