Fixes utf8 conversions with ruby1.9.

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@4605 e93f8b46-1217-0410-a6f0-8f06a7374b81

app/helpers/attachments_helper.rb

@@ -29,7 +29,13 @@ module AttachmentsHelper
   end
   
   def to_utf8(str)
-    return str if /\A[\r\n\t\x20-\x7e]*\Z/n.match(str) # for us-ascii
+    if str.respond_to?(:force_encoding)
+      str.force_encoding('UTF-8')
+      return str if str.valid_encoding?
+    else
+      return str if /\A[\r\n\t\x20-\x7e]*\Z/n.match(str) # for us-ascii
+    end
+    
     begin
       Iconv.conv('UTF-8//IGNORE', 'UTF-8', str + '  ')[0..-3]
     rescue Iconv::InvalidEncoding