UI: liquid level widget added additional checkup for datasources

ui-ngx/src/app/modules/home/components/widget/lib/indicator/liquid-level-widget.component.ts

@@ -160,6 +160,7 @@ export class LiquidLevelWidgetComponent implements OnInit {
   }
 
   private getData(): Observable<{ svg: string; volume: number; units: string }> {
+    if (this.ctx.datasources?.length) {
       const entityId: EntityId = {
         entityType: this.ctx.datasources[0].entityType,
         id: this.ctx.datasources[0].entityId
@@ -182,6 +183,9 @@ export class LiquidLevelWidgetComponent implements OnInit {
       );
     }
 
+    return of(null);
+  }
+
   public onInit() {
     const borderRadius = this.ctx.$widgetElement.css('borderRadius');
     this.overlayStyle = {...this.overlayStyle, ...{borderRadius}};