hide keywords if no keywords exists

src/app/components/shared/comment/comment.component.html

@@ -320,6 +320,7 @@
       <div fxLayoutAlign="center center"
            matTooltip="{{ 'comment-page.keywords-per-question' | translate }}"
            [mat-menu-trigger-for]="keywordsMenu"
+           *ngIf="(comment.keywords != undefined && comment.keywords.length > 0)"
            class="comment-keywords">
         <mat-icon svgIcon="comment_tag"></mat-icon>
         <span>