FIX: Select correct topic draft for user (#15234)

The old query could return multiple rows.

app/models/user_stat.rb

@@ -211,7 +211,7 @@ class UserStat < ActiveRecord::Base
         UPDATE user_stats
         SET draft_count = (SELECT COUNT(*) FROM drafts WHERE user_id = :user_id)
         WHERE user_id = :user_id
-        RETURNING draft_count, (SELECT 1 FROM drafts WHERE draft_key = :new_topic)
+        RETURNING draft_count, (SELECT 1 FROM drafts WHERE user_id = :user_id AND draft_key = :new_topic)
       SQL
 
       MessageBus.publish(

spec/models/draft_spec.rb

@@ -179,6 +179,8 @@ describe Draft do
   end
 
   it 'updates draft count when a draft is created or destroyed' do
+    Draft.set(Fabricate(:user), Draft::NEW_TOPIC, 0, "data")
+
     messages = MessageBus.track_publish("/user") do
       Draft.set(user, Draft::NEW_TOPIC, 0, "data")
     end