FIX: Avoid rescuing error in login hint initializer.

On the first migration, trying to access the users table will throw an
error in PostgreSQL's log which has been confusing since users will
report it to us when rebuild fails.

config/initializers/006-ensure_login_hint.rb

@@ -1,5 +1,8 @@
 # Some sanity checking so we don't count on an unindexed column on boot
-if User.limit(20).count < 20 && User.where(admin: true).human_users.count == 0
+if ActiveRecord::Base.connection.table_exists?(:users) &&
+   User.limit(20).count < 20 &&
+   User.where(admin: true).human_users.count == 0
+
   notice =
     if GlobalSetting.developer_emails.blank?
       "Congratulations, you installed Discourse! Unfortunately, no administrator emails were defined during setup, so finalizing the configuration <a href='https://meta.discourse.org/t/create-admin-account-from-console/17274'>may be difficult</a>."
@@ -17,6 +20,4 @@ if User.limit(20).count < 20 && User.where(admin: true).human_users.count == 0
     SiteSetting.global_notice = notice
     SiteSetting.has_login_hint = true
   end
-
-  # we may be booting with no User table eg: first migration, just skip
-end rescue nil
+end