@Override
	public boolean isStartDragOk(DragGestureEvent e) {
		int row = table.rowAtPoint(e.getDragOrigin());
		if (row >= 0) {
			return true;
		}
		return false;
	}
Get the selected version number or {@link DomainFile#DEFAULT_VERSION} if no selection.
@return selected version number
Ghidra/Framework/Project/src/main/java/ghidra/framework/main/datatree/VersionHistoryPanel.java