status-area: Handle clients that don't provide icon_name/icon_pixmap

It seems some clients expose the properties and leave them empty, but
others just provide either one on its own.

This fixes clients like Mattermost.

cosmic-applet-status-area/src/subscriptions/status_notifier_item.rs

@@ -33,10 +33,11 @@ impl StatusNotifierItem {
             .build()
             .await?;
 
-        let icon_name = item_proxy.icon_name().await?;
+        let icon_name = item_proxy.icon_name().await.unwrap_or_default();
         let icon_pixmap = item_proxy
             .icon_pixmap()
-            .await?
+            .await
+            .unwrap_or_default()
             .into_iter()
             .max_by_key(|i| (i.width, i.height))
             .map(|mut i| {