Bug 260892 [CellEditors] NPE from ColumnViewerEditor caused by showing a dialog during modify
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/ColumnViewerEditor.java
if( ! this.cell.getItem().isDisposed() ) {
						this.cell.getItem().removeDisposeListener(disposeListener);
					}
				}
				this.cellEditor = null;
				this.cell = null;
			} finally {
				inEditorDeactivation = false;
			}
		}
	}
	/**
	 * Cancel editing
	 */
	void cancelEditing() {
		
		if (!inEditorDeactivation) {
			try {
				inEditorDeactivation = true;
				if (cellEditor != null) {
					ColumnViewerEditorDeactivationEvent tmp = new ColumnViewerEditorDeactivationEvent(
							cell);
					tmp.eventType = ColumnViewerEditorDeactivationEvent.EDITOR_CANCELED;
					if (editorActivationListener != null
							&& !editorActivationListener.isEmpty()) {
						Object[] ls = editorActivationListener.getListeners();
						for (int i = 0; i < ls.length; i++) {
							((ColumnViewerEditorActivationListener) ls[i])
									.beforeEditorDeactivated(tmp);