Add extra safety

app/controllers/static_controller.rb

@@ -93,13 +93,21 @@ class StaticController < ApplicationController
   # a huge expiry, we also cache these assets in nginx so it bypassed if needed
   def favicon
 
-    data = DistributedMemoizer.memoize('favicon' + SiteSetting.favicon_url, 60*60*24) do
+    data = DistributedMemoizer.memoize('favicon' + SiteSetting.favicon_url, 60*30) do
+      begin
         file = FileHelper.download(SiteSetting.favicon_url, 50.kilobytes, "favicon.png")
         data = file.read
         file.unlink
         data
+      rescue => e
+        Rails.logger.warn("Invalid favicon_url #{SiteSetting.favicon_url}: #{e}\n#{e.backtrace}")
+        ""
+      end
     end
 
+    if data.bytesize == 0
+      render text: UserAvatarsController::DOT, content_type: "image/gif"
+    else
       expires_in 1.year, public: true
       response.headers["Expires"] = 1.year.from_now.httpdate
       response.headers["Content-Length"] = data.bytesize.to_s
@@ -107,6 +115,8 @@ class StaticController < ApplicationController
       render text: data, content_type: "image/png"
     end
 
+  end
+
 
   def cdn_asset
     path = File.expand_path(Rails.root + "public/assets/" + params[:path])