DDTabSheet loses tabs

[ariordan]

When transferring a tab between two DDtabSheets using DefaultTabSheetDropHandler, it is possible to lose the dragged tab. This occurs when HorizontalDropLocation (location) is null, which occurs when the tab is dragged over the content of the other tabsheet, rather then the tabsheet tabs.

There are two possible solutions to this issue:

1: do not perform the drag when location is null

---

protected void handleDropFromLayout(DragAndDropEvent event) {
    ....
    // cancel drag if location is null
    if (location == null) {
        return;
    }

    if(source instanceof ComponentContainer) {
        source.removeComponent(c);
    } else if(source instanceof SingleComponentContainer) {
        ((SingleComponentContainer)source).setContent((Component)null);
    }
    ....
}

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2: append the tab to the end of the target tabsheets tab list

---

protected void handleDropFromLayout(DragAndDropEvent event) {
    ...
    if(location == HorizontalDropLocation.LEFT) {
        tabSheet.addTab(c, idx);
    } else if(location == HorizontalDropLocation.RIGHT) {
        tabSheet.addTab(c, idx + 1);

    // add tab to end of tab list if location is null
    } else {
        tabSheet.addTab(c);
    }
}

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