Merge branch 'ee_empty_brand_image' into 'master'

empty brand image are displayed as empty image_tag on login page

When using a custom appearance without uploading an image, an empty HTML img-tag is rendered, showing up badly in some browsers: http://i.imgur.com/EN9WpuA.png
Also, the empty img-tag was rendered in the admin/appearance form.

app/helpers/appearances_helper.rb

@@ -8,13 +8,15 @@ module AppearancesHelper
   end
 
   def brand_image
-    logo = if brand_item
-             brand_item.logo
-           else
-             'brand_logo.png'
-           end
-
-    image_tag logo
+    if brand_item
+      if brand_item.logo?
+        image_tag brand_item.logo
+      else
+        nil
+      end
+    else
+      image_tag 'brand_logo.png'
+    end
   end
 
   def brand_text

app/views/admin/appearances/_form.html.haml

@@ -17,7 +17,7 @@
   .form-group
     = f.label :logo, class: 'control-label'
     .col-sm-10
-      - if @appearance.logo
+      - if @appearance.logo?
         = image_tag @appearance.logo, class: 'appearance-logo-preview'
       = f.file_field :logo, class: ""
       .hint