fix(useSortable): prevent from creating multi instances

[Doctor-wu]

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Description

fix #3496
prevent start multi instance

Additional context

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🤖 Generated by Copilot at 9afb592

This pull request fixes a bug in onClickOutside and improves the performance and reliability of useSortable. It ensures that the onClickOutside function correctly handles null or undefined target elements, and that the useSortable function does not create duplicate Sortable instances.

🤖 Generated by Copilot at 9afb592

• Fix a bug in onClickOutside that caused incorrect shouldListen value when target element was null or undefined (link)
• Prevent creating duplicate Sortable instances in useSortable by checking if one already exists for the target element (link)

[Alfred-Skyblue]

We should set sortable to undefined when stopping, and when starting, we should check if sortable exists; if it does, we should not create a new sortable.

[Doctor-wu]

We should set sortable to undefined when stopping, and when starting, we should check if sortable exists; if it does, we should not create a new sortable.

@Alfred-Skyblue Got you, so I think we need to set the sortable to undefined when the stop function is invoked

[brgkcosic]

does this inherently then stop from creating recursive groups that can be sorted? I need to implement a functionality that groups items inside, and this group can either render a group item or another group (recursively) - so my logic is to create groups that are sortable and eventual rendering of items when reaching the bottom line.

[Alfred-Skyblue]

@brgkcosic If you need to perform recursive sorting, you should create a separate sortable instance at each level of recursion.