feat: better display of region loading

src/atlasComponents/parcellationRegion/regionMenu/regionMenu.template.html

+<ng-template [ngIf]="region">
+
 <mat-card class="mat-elevation-z4">
   <!-- rgbDarkmode must be checked for strict equality to true/false 
   as if rgb is undefined, rgbDarkmode will be null/undefined
@@ -218,3 +220,16 @@
     </ng-template>
   </mat-expansion-panel>
 </ng-template>
+</ng-template>
+
+
+<ng-template [ngIf]="!region">
+  <mat-card class="mat-elevation-z4">
+    <h1 class="mat-h1 sidenav-cover-header-container">
+      <spinner-cmp class="d-inline-block"></spinner-cmp>
+      <span class="text-muted">
+        Loading region
+      </span>
+    </h1>
+  </mat-card>
+</ng-template>
\ No newline at end of file

src/viewerModule/viewerCmp/viewerCmp.component.ts

 import { Component, ElementRef, Inject, Input, OnDestroy, Optional, TemplateRef, ViewChild } from "@angular/core";
 import { select, Store } from "@ngrx/store";
 import {combineLatest, Observable, of, Subject, Subscription} from "rxjs";
-import {distinctUntilChanged, filter, map, shareReplay, startWith, switchMap } from "rxjs/operators";
+import {catchError, distinctUntilChanged, filter, map, shareReplay, startWith, switchMap } from "rxjs/operators";
 import { viewerStateSetSelectedRegions } from "src/services/state/viewerState/actions";
 import {
   viewerStateContextedSelectedRegionsSelector,
@@ -77,6 +77,8 @@ import { ContextMenuService, TContextMenuReg } from "src/contextMenuModule";
                 context
               }
             }),
+            // in case detailed requests 
+            catchError((err, obs) => of(r[0])),
             shareReplay(1),
           )
         })

src/viewerModule/viewerCmp/viewerCmp.template.html

@@ -474,12 +474,10 @@
 <!-- single region tmpl -->
 <ng-template #singleRegionTmpl let-region="region">
   <!-- region detail -->
-  <ng-container *ngIf="region; else regionPlaceholderTmpl">
-    <region-menu
-      [region]="region"
-      class="flex-grow-1 bs-border-box ml-15px-n mr-15px-n mat-elevation-z4">
-    </region-menu>
-  </ng-container>
+  <region-menu
+    [region]="region"
+    class="flex-grow-1 bs-border-box ml-15px-n mr-15px-n mat-elevation-z4">
+  </region-menu>
 </ng-template>