Show "no info" message when we don't have infos about roles.

web/i18n/en.yml

@@ -228,6 +228,7 @@ pages:
             nodes_tooltip: Relation members of type node with this role (and as percentage of all members of type node) for this relation type.
             ways_tooltip: Relation members of type way with this role (and as percentage of all members of type way) for this relation type.
             relations_tooltip: Relation members of type relation with this role (and as percentage of all members of type relation) for this relation type.
+            no_roles_info: There is no information about roles for this relation type (most likely because there are only very few of those relations).
 
 flexigrid:
     pagetext: Page

web/lib/ui/relation.rb

@@ -13,6 +13,10 @@ class Taginfo < Sinatra::Base
 
         @desc = 'XXX'
 
+        @count_relation_roles = @db.count('relation_roles').
+            condition("rtype=?", rtype).
+            get_first_value().to_i
+
         javascript "#{ r18n.locale.code }/relation"
         erb :relation
     end

web/views/relation.erb

@@ -12,8 +12,12 @@
     </div>
     <div id="roles">
         <h2><%= t.pages.relation.roles.title %></h2>
+<% if @count_relation_roles > 0 %>
         <table id="grid-roles">
         </table>
+<% else %>
+        <p class="empty"><%= t.pages.relation.roles.no_roles_info %></p>
+<% end %>
     </div>
 </div>
 <% javascript do