Fix error when rendering non-ASCII ReadMe files

[stanclai]

Avoid crash on ReadMe files containing non-ASCII symbols

Without such workaround this module constantly caused Server Error 500 in repository view with the following log dump, if the repo contained ReadMe file in UTF-8 codepage:

  Rendered plugins/redmine_git_hosting/app/views/repositories/show.html.erb within layouts/base (191.4ms)
Completed 500 Internal Server Error in 303ms (ActiveRecord: 30.8ms)                            

ActionView::Template::Error ("\xE2" from ASCII-8BIT to UTF-8):
    47:                        :id => @project, :page => nil, :key => User.current.rss_key})) %>
    48:    <% end %>
    49:
    50:    <%= call_hook(:view_repositories_show_bottom) %>
    51:
    52:    <% other_formats_links do |f| %>
    53:     <%= f.link_to 'Atom',
  lib/redmine/hook.rb:61:in `block (2 levels) in call_hook'
  lib/redmine/hook.rb:61:in `each'
  lib/redmine/hook.rb:61:in `block in call_hook'
  lib/redmine/hook.rb:58:in `tap'
  lib/redmine/hook.rb:58:in `call_hook'
  lib/redmine/hook.rb:158:in `call_hook'
  app/controllers/repositories_controller.rb:125:in `show'

[n-rodriguez]

Thank you!

[stanclai]

No problem :)