server list: show generic server icon if server doesn't provide one

VLC for Apple TV/Assets.xcassets/NetworkBrowsing/serverIcon.imageset/Contents.json

+{
+  "images" : [
+    {
+      "idiom" : "tv",
+      "filename" : "serverIcon@3x.png",
+      "scale" : "1x"
+    }
+  ],
+  "info" : {
+    "version" : 1,
+    "author" : "xcode"
+  }
+}
\ No newline at end of file

VLC for Apple TV/VLCServerListTVTableViewController.m

@@ -99,7 +99,7 @@
     UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:VLCLocalServerTVCell forIndexPath:indexPath];
     id<VLCLocalNetworkService> service = [self.discoveryController networkServiceForIndexPath:indexPath];
     cell.textLabel.text = service.title;
-    cell.imageView.image = service.icon;
+    cell.imageView.image = service.icon ? service.icon : [UIImage imageNamed:@"serverIcon"];
     return cell;
 }