Review widget: fix error in node deletion handling

After node deletion, the review segment showed an error if a subarbor
was under review. This is fixed now by checking if there is a subarbor
under review in the first place, before attempting to refer to it.

Second, the view isn't moved anymore after a node was deleted. As
@acardona pointed out, this is rather distracting and one is usually
well aware where one deletes a node. Plus, returning to the node under
review can be achieved by W/E key presses or by clicking on the "Review"
button.

See catmaid/catmaid@2280

Author: tomka

django/applications/catmaid/static/js/widgets/review.js

@@ -107,9 +107,11 @@
     this.handleDeletedSkeleton = function(nodeId, parentId, skeletonId) {
       if (skeletonId == this.currentSkeletonId) {
         CATMAID.info('Review widget updated due to skeleton change');
-        this.startSkeletonToReview(skeletonId, undefined, true, () => {
-          this.current_segment = this.skeleton_segments[this.current_segment.id];
-          this.goToNodeIndexOfSegmentSequence(this.current_segment_index, true);
+        this.startSkeletonToReview(skeletonId, this.currentSubarborNodeId, true, () => {
+          if (this.current_segment) {
+            // Reload data, in case the deleted node was part of this segment
+            this.current_segment = this.skeleton_segments[this.current_segment.id];
+          }
         });
       }
     };