FIX: merge votes regardless of voters' visibility (#187)

Ensures merging topics also merges votes regardless of the voters' visibility (when voting_show_who_voted site setting is false).

plugin.rb

@@ -179,8 +179,9 @@ class Engine < ::Rails::Engine
     moved_votes = 0
     duplicated_votes = 0
 
-    if orig.who_voted.present? && orig.closed
-      orig.who_voted.each do |user|
+    who_voted = orig.votes.map(&:user)
+    if who_voted.present? && orig.closed
+      who_voted.each do |user|
         next if user.blank?
 
         user_votes = user.topics_with_vote.pluck(:topic_id)

spec/voting_spec.rb

@@ -36,6 +36,9 @@
     let(:users) { [user0, user1, user2, user3, user4, user5] }
 
     before do
+      # ensure merging votes works regardless of voters' visibility
+      SiteSetting.voting_show_who_voted = false
+
       Fabricate(:post, topic: topic0, user: user0)
       Fabricate(:post, topic: topic0, user: user0)