Add 'nothing to preview' message

app/assets/stylesheets/content/_preview.css.sass

@@ -0,0 +1,30 @@
+/*-- copyright
+ * OpenProject is a project management system.
+ * Copyright (C) 2012-2013 the OpenProject Foundation (OPF)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License version 3.
+ *
+ * OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+ * Copyright (C) 2006-2013 Jean-Philippe Lang
+ * Copyright (C) 2010-2013 the ChiliProject Team
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ *
+ * See doc/COPYRIGHT.rdoc for more details.  ++
+ */
+
+.nothing-to-preview
+  color: red

app/assets/stylesheets/default.css.sass

@@ -55,4 +55,5 @@
 @import content/tabular
 @import content/headings
 @import content/timelines
+@import content/preview
 @import default/main

app/views/common/preview.html.erb

@@ -27,8 +27,14 @@ See doc/COPYRIGHT.rdoc for more details.
 
 ++#%>
 
-<% texts.each do |text| %>
+<% if texts.empty? %>
   <fieldset class="preview"><legend><%= l(:label_preview) %></legend>
-    <%= textilizable text, attachments: attachments, object: previewed %>
+    <span class="nothing-to-preview"><%= l(:nothing_to_preview) %></span>
   </fieldset>
+<% else %>
+  <% texts.each do |text| %>
+    <fieldset class="preview"><legend><%= l(:label_preview) %></legend>
+      <%= textilizable text, attachments: attachments, object: previewed %>
+    </fieldset>
+  <% end %>
 <% end %>

config/locales/de.yml

@@ -1653,3 +1653,5 @@ de:
   work_package:
     updated_automatically_by_child_changes: |
         _Automatisch durch die Änderungen in %{child} aktualisert_
+
+  nothing_to_preview: "Keine Inhalte für Vorschau vorhanden"

config/locales/en.yml

@@ -1640,3 +1640,5 @@ en:
   work_package:
     updated_automatically_by_child_changes: |
         _Updated automatically by changing values within child work package %{child}_
+
+  nothing_to_preview: "Nothing to preview"