Fixes #13968 - Fail to save proxy if feature is missing

app/models/smart_proxy.rb

@@ -115,16 +115,20 @@ def associate_features
 
     begin
       reply = ProxyAPI::Features.new(:url => url).features
-      if reply.is_a?(Array) && reply.any?
+      if reply.is_a?(Array) && reply.any? && validate_features(reply)
         self.features = Feature.where(:name => reply.map{|f| Feature.name_map[f]})
       else
         self.features.clear
-        errors.add :base, _('No features found on this proxy, please make sure you enable at least one feature')
+        errors.add :base, _('No matching features found on this proxy, please make sure you enable at least one feature')
       end
     rescue => e
       errors.add(:base, _('Unable to communicate with the proxy: %s') % e)
       errors.add(:base, _('Please check the proxy is configured and running on the host.'))
     end
     features.any?
   end
+
+  def validate_features(features)
+    features.map{|f| Feature.name_map[f]} == nil
+  end
 end