Next button remains enabled when no items are selected after toggling "Hide items that are already installed" #1036
Description
Steps to replicate
- Open Help → Install New Software…
- Select an update site that contains installable plugins.
- Click Select All or manually select any plugin from the list.
- Enable the checkbox "Hide items that are already installed".
- Observe the plugin list and selection state and the Next button.
Expected Behavior
If no plugins are visibly selected (all checkboxes unchecked), the Next button should be disabled.