Fix an error when TagManager.local_url? is called with a bad URI (#3701)

TagManager.local_url? was sometimes called with an URI with a nil host,
leading to a crash in TagManager.local_url?. This fixes moves the
already-existing uri.host.blank? check in front to avoid this case.

app/services/fetch_link_card_service.rb

@@ -36,7 +36,7 @@ class FetchLinkCardService < BaseService
 
   def bad_url?(uri)
     # Avoid local instance URLs and invalid URLs
-    TagManager.instance.local_url?(uri.to_s) || !%w(http https).include?(uri.scheme) || uri.host.blank?
+    uri.host.blank? || TagManager.instance.local_url?(uri.to_s) || !%w(http https).include?(uri.scheme)
   end
 
   def skip_link?(a)