Fix "Widget is disposed" exception in VisibleLinesTracker#3376

vogella merged 1 commit intoeclipse-platform:mastereclipse-platform/eclipse.platform.ui:masterfrom

wahlbrink:fix-WidgetDisposed-VisibleLinesTrackerwahlbrink/eclipse.platform.ui:fix-WidgetDisposed-VisibleLinesTrackerCopy head branch name to clipboard