feat(segmentation mode): Add create, and export SEG with Brushes (#3632)

extensions/cornerstone-dicom-sr/src/viewports/OHIFCornerstoneSRViewport.tsx

@@ -240,7 +240,7 @@ function OHIFCornerstoneSRViewport(props) {
     const onDisplaySetsRemovedSubscription = displaySetService.subscribe(
       displaySetService.EVENTS.DISPLAY_SETS_REMOVED,
       ({ displaySetInstanceUIDs }) => {
-        const activeViewport = viewports[activeViewportId];
+        const activeViewport = viewports.get(activeViewportId);
         if (displaySetInstanceUIDs.includes(activeViewport.displaySetInstanceUID)) {
           viewportGridService.setDisplaySetsForViewport({
             viewportId: activeViewportId,