Template error when user's timezone isn't set and UTC timestamps are used (#1889).

git-svn-id: http://redmine.rubyforge.org/svn/trunk@1801 e93f8b46-1217-0410-a6f0-8f06a7374b81

app/models/user.rb

@@ -144,7 +144,7 @@ class User < ActiveRecord::Base
   end
   
   def time_zone
-    self.pref.time_zone.nil? ? nil : TimeZone[self.pref.time_zone]
+    @time_zone ||= (self.pref.time_zone.blank? ? nil : TimeZone[self.pref.time_zone])
   end
   
   def wants_comments_in_reverse_order?