FIX: StaticController#favicon reads from disk when using local store. (#7160)

Since uploads site settings are now backed by an actual upload, we don't
have to reach over the network just to fetch the favicon. Instead, we
can just read the upload directly from disk.

app/controllers/static_controller.rb

@@ -124,22 +124,28 @@ class StaticController < ApplicationController
     is_asset_path
 
     hijack do
-      data = DistributedMemoizer.memoize(FAVICON + SiteSetting.site_favicon_url, 60 * 30) do
-        begin
-          file = FileHelper.download(
-            UrlHelper.absolute(SiteSetting.site_favicon_url),
-            max_file_size: 50.kilobytes,
-            tmp_file_name: FAVICON,
-            follow_redirect: true
-          )
-          file ||= Tempfile.new([FAVICON, ".png"])
-          data = file.read
-          file.unlink
-          data
-        rescue => e
-          AdminDashboardData.add_problem_message('dashboard.bad_favicon_url', 1800)
-          Rails.logger.debug("Invalid favicon_url #{SiteSetting.site_favicon_url}: #{e}\n#{e.backtrace}")
-          ""
+      data = DistributedMemoizer.memoize("FAVICON#{SiteSetting.favicon&.id}", 60 * 30) do
+        favicon = SiteSetting.favicon
+        next "" unless favicon
+
+        if Discourse.store.external?
+          begin
+            file = FileHelper.download(
+              UrlHelper.absolute(favicon.url),
+              max_file_size: favicon.filesize,
+              tmp_file_name: FAVICON,
+              follow_redirect: true
+            )
+
+            file&.read || ""
+          rescue => e
+            AdminDashboardData.add_problem_message('dashboard.bad_favicon_url', 1800)
+            Rails.logger.warn("Failed to fetch faivcon #{favicon.url}: #{e}\n#{e.backtrace}")
+          ensure
+            file&.unlink
+          end
+        else
+          File.read(Rails.root.join("public", favicon.url[1..-1]))
         end
       end