Widget is disposed during refresh call in virtual tree

[laeubi]

!ENTRY org.eclipse.e4.ui.workbench 4 0 2026-02-08 14:07:18.904
!MESSAGE Internal Error
!STACK 0
org.eclipse.swt.SWTException: Widget is disposed
	at org.eclipse.swt.SWT.error(SWT.java:4950)
	at org.eclipse.swt.SWT.error(SWT.java:4865)
	at org.eclipse.swt.SWT.error(SWT.java:4836)
	at org.eclipse.swt.widgets.Widget.error(Widget.java:598)
	at org.eclipse.swt.widgets.Widget.checkWidget(Widget.java:513)
	at org.eclipse.swt.widgets.TreeItem.getItems(TreeItem.java:806)
	at org.eclipse.jface.viewers.TreeViewer.getChildren(TreeViewer.java:163)
	at org.eclipse.jface.viewers.TreeViewer.virtualRefreshExpandedItems(TreeViewer.java:707)
	at org.eclipse.jface.viewers.TreeViewer.internalRefreshStruct(TreeViewer.java:680)
	at org.eclipse.jface.viewers.AbstractTreeViewer.internalRefresh(AbstractTreeViewer.java:2005)
	at org.eclipse.jface.viewers.AbstractTreeViewer.internalRefresh(AbstractTreeViewer.java:1962)
	at org.eclipse.jface.viewers.AbstractTreeViewer.internalRefresh(AbstractTreeViewer.java:1948)
	at org.eclipse.jface.viewers.StructuredViewer.lambda$2(StructuredViewer.java:1466)
	at org.eclipse.jface.viewers.StructuredViewer.preservingSelection(StructuredViewer.java:1395)
	at org.eclipse.jface.viewers.TreeViewer.preservingSelection(TreeViewer.java:368)
	at org.eclipse.jface.viewers.StructuredViewer.preservingSelection(StructuredViewer.java:1356)
	at org.eclipse.jface.viewers.StructuredViewer.refresh(StructuredViewer.java:1466)
	at org.eclipse.jface.viewers.ColumnViewer.refresh(ColumnViewer.java:521)

This seem to happen when an item is refreshed whose internal tree item mapping is already removed, leading to an ugly error dialog shown. TreeViewer.getChildren should check if the TreeItem is not already disposed in the meanwhile.