FIX: handle concurrently creating post reply keys

In some very rare conditions this would be called concurrently and fail

lib/email/sender.rb

@@ -262,7 +262,8 @@ module Email
         post_id &&
         header_value(Email::MessageBuilder::ALLOW_REPLY_BY_EMAIL_HEADER).present?
 
-      reply_key = PostReplyKey.find_or_create_by!(
+      # use safe variant here cause we tend to see concurrency issue
+      reply_key = PostReplyKey.find_or_create_by_safe!(
         post_id: post_id,
         user_id: user_id
       ).reply_key

lib/freedom_patches/active_record_base.rb

@@ -1,5 +1,17 @@
 class ActiveRecord::Base
 
+  # Handle PG::UniqueViolation as well due to concurrency
+  # find_or_create does find_by(hash) || create!(hash)
+  # in some cases find will not find and multiple creates will be called
+  def self.find_or_create_by_safe!(hash)
+    begin
+      find_or_create_by!(hash)
+    rescue PG::UniqueViolation
+      # try again cause another transaction could have passed by now
+      find_or_create_by!(hash)
+    end
+  end
+
   # Execute SQL manually
   def self.exec_sql(*args)