Don't try to display ugoira thumbnail/webm before they exist

app/models/post.rb

@@ -154,7 +154,7 @@ class Post < ActiveRecord::Base
     end
 
     def has_ugoira_webm?
-      created_at < 1.minute.ago || File.exists?(preview_file_path) 
+      created_at < 1.minute.ago || (File.exists?(preview_file_path) && File.size(preview_file_path) > 0)
     end
   end
 

app/views/posts/partials/show/_ugoira.html.erb

@@ -1,4 +1,4 @@
-<% if CurrentUser.user.default_image_size == "large" && params[:original].blank? %>
+<% if CurrentUser.user.default_image_size == "large" && params[:original].blank? && post.has_ugoira_webm? %>
   <%= render "posts/partials/show/ugoira_webm", :post => post %>
 <% else %>
   <%= render "posts/partials/show/ugoira_original", :post => post %>