scm: set empty log encoding UTF-8 in Ruby 1.9 and add tests.

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@5368 e93f8b46-1217-0410-a6f0-8f06a7374b81

app/models/changeset.rb

@@ -247,7 +247,10 @@ class Changeset < ActiveRecord::Base
   def self.to_utf8(str, encoding)
     return str if str.nil?
     str.force_encoding("ASCII-8BIT") if str.respond_to?(:force_encoding)
-    return str if str.empty?
+    if str.empty?
+      str.force_encoding("UTF-8") if str.respond_to?(:force_encoding)
+      return str
+    end
     str.force_encoding("UTF-8") if str.respond_to?(:force_encoding)
     if str.respond_to?(:force_encoding)
       enc = encoding.blank? ? "UTF-8" : encoding