[polari] urlPreview: Show fallback image on failure

[Florian Müllner <fmuellner src gnome org>]

commit 05c8269c6fb09e4f5b9ba18ca77774d833034145
Author: Florian Müllner <fmuellner gnome org>
Date:   Thu Jul 30 00:45:38 2020 +0200

    urlPreview: Show fallback image on failure
    
    We should only show the loading indicator when we are actually
    loading the image, not when the operation completed but failed.
    Switch to an appropriate fallback in that case.
    
    https://gitlab.gnome.org/GNOME/polari/-/issues/149

 src/urlPreview.js | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)
---
diff --git a/src/urlPreview.js b/src/urlPreview.js
index 88cf9d2e..5ff426f6 100644
--- a/src/urlPreview.js
+++ b/src/urlPreview.js
@@ -103,9 +103,9 @@ var URLPreview = GObject.registerClass({
 
         this._imageLoaded = false;
         this._image = new Gtk.Image({
-            icon_name: 'image-loading-symbolic',
             visible: true,
         });
+        this._image.get_style_context().add_class('dim-label');
         this.add(this._image);
 
         this._label = new Gtk.Label({
@@ -122,6 +122,10 @@ var URLPreview = GObject.registerClass({
             return;
 
         this._imageLoaded = true;
+        this._image.set({
+            icon_name: 'image-loading-symbolic',
+            pixel_size: 16,
+        });
         const thumbnailer = Thumbnailer.getDefault();
 
         try {
@@ -129,6 +133,10 @@ var URLPreview = GObject.registerClass({
             this._image.set_from_file(filename);
         } catch (e) {
             log(`Thumbnail generation for ${this.uri} failed: ${e}`);
+            this._image.set({
+                icon_name: 'image-x-generic-symbolic',
+                pixel_size: 64,
+            });
         }
 
         let title = null;