utc_offset returns nil for unknown zones

Signed-off-by: Jeremy Kemper <jeremy@bitsweat.net>

activesupport/lib/active_support/values/time_zone.rb

@@ -1,4 +1,5 @@
 require 'active_support/core_ext/object/blank'
+require 'active_support/core_ext/object/try'
 
 # The TimeZone class serves as a wrapper around TZInfo::Timezone instances. It allows us to do the following:
 #
@@ -205,8 +206,8 @@ module ActiveSupport
       if @utc_offset
         @utc_offset
       else
-        @current_period ||= tzinfo.current_period
-        @current_period.utc_offset
+        @current_period ||= tzinfo.try(:current_period)
+        @current_period.try(:utc_offset)
       end
     end
 

activesupport/test/time_zone_test.rb

@@ -274,9 +274,15 @@ class TimeZoneTest < Test::Unit::TestCase
     assert_raise(ArgumentError) { ActiveSupport::TimeZone[false] }
   end
 
-  def test_unknown_zone_shouldnt_have_tzinfo
+  def test_unknown_zone_shouldnt_have_tzinfo_nor_utc_offset
     zone = ActiveSupport::TimeZone.create("bogus")
     assert_nil zone.tzinfo
+    assert_nil zone.utc_offset
+  end
+
+  def test_unknown_zone_with_utc_offset
+    zone = ActiveSupport::TimeZone.create("bogus", -21_600)
+    assert_equal -21_600, zone.utc_offset
   end
 
   def test_new