favorites: fix users with incorrect favorite counts.

Fix users that have a non-zero favorite count, but no favorites.
Follow-up to 69facb22b.

app/models/user.rb

@@ -602,6 +602,10 @@ class User < ApplicationRecord
 
     class_methods do
       def fix_favorite_counts!
+        # Fix users that have a non-zero favorite_count but no favorites.
+        User.where("favorite_count != 0").where.not(id: Favorite.select(:user_id).distinct).update_all(favorite_count: 0)
+
+        # Fix users that have a favorite_count inconsistent with the favorites table.
         User.find_by_sql(<<~SQL.squish)
           UPDATE users
           SET favorite_count = true_count