Fix for chinese-title-file

[keineahnung2345]

1. change title to utf8 encoding solves:

   
   ActionView::Template::Error (incompatible character encodings: ASCII-8BIT and UTF-8):
   91:           <% end %>
   92:           <%= content_tag('span', h(e.format_identifier), class: 'identifier') if defined?(e.format_identifier) && !e.format_identifier.empty? %>
   93:           <% # end %>
   94:           <%= link_to(highlight_tokens(e.event_title.truncate(255), @tokens), e.event_url) %>
   95:         </dt>
   96:         <dd><span class="description"><%= highlight_tokens(e.event_description, @tokens) %></span>
   97:         <span class="author"><%= format_time(e.event_datetime) %></span></dd>

plugins/redmine_xapian/app/views/search/index.html.erb:94:in block in _dec9f35c6d83bf3080fd2d9ef7734b5b' plugins/redmine_xapian/app/views/search/index.html.erb:82:ineach' plugins/redmine_xapian/app/views/search/index.html.erb:82:in _dec9f35c6d83bf3080fd2d9ef7734b5b' lib/redmine/sudo_mode.rb:65:insudo_mode'

2. In my case, my `url` is already prepended with `File.join Redmine::Utils::relative_url_root`, so `url = File.join Redmine::Utils::relative_url_root, url` is redundant(don't know if it's such case for other people)
  My `config/environment.rb`:
    ```ruby
    ActionController::Base.relative_url_root = RedmineApp::Application.routes.default_scope
    Redmine::Utils::relative_url_root = RedmineApp::Application.routes.default_scope

    ENV['RAILS_RELATIVE_URL_ROOT'] = "/redmine"
    Redmine::Utils::relative_url_root = ENV['RAILS_RELATIVE_URL_ROOT']

My `config.ru`:
```ruby
map ENV['RAILS_RELATIVE_URL_ROOT'] || '/' do
  run Rails.application
end
```
My `config/additional_environment.rb`:
```ruby
config.relative_url_root = '/redmine'
```

3. change url to utf8 encoding solves Wrong format of the URL for chinese title file

[picman]

Thank you.