Fix page display after receiving data from backend.

frontend/src/app/pages/publication/publication.component.html

@@ -1,8 +1,8 @@
-@if (isLoading) {
+@if (isLoading()) {
     <h2 i18n>Publication content loading...</h2>
     <mat-spinner></mat-spinner>
 } @else {
-    @if (publication) {
+    @if (publication(); as publication) {
         <div class="card">
             <img src="/api/pictures/{{ publication.illustrationId }}" />
             <header>
@@ -32,7 +32,7 @@
                 @if (isAuthorAndUserEquals) {
                     <button type="button"
                         (click)="deletePublication()"
-                        matTooltip="Click to delete the publication" 
+                        matTooltip="Click to delete the publication"
                         matTooltipPosition="left"
                         matRipple
                         i18n-matTooltip>
@@ -47,4 +47,4 @@
             <h1 i18n>Publication failed to load...</h1>
         </div>
     }
-}
+}