Fix #3613: Broken preview images for flash files.

app/logical/storage_manager.rb

@@ -54,7 +54,7 @@ class StorageManager
     seo_tags = seo_tags(post) if tagged_filenames
 
     if type == :preview && !post.has_preview?
-      "#{base_url}/images/download-preview.png"
+      "#{root_url}/images/download-preview.png"
     elsif type == :preview
       "#{base_url}/preview/#{subdir}#{file}"
     elsif type == :large && post.has_large?
@@ -66,6 +66,12 @@ class StorageManager
 
   protected
 
+  def root_url
+    origin = Addressable::URI.parse(base_url).origin
+    origin = "" if origin == "null" # base_url was relative
+    origin
+  end
+
   def file_path(md5, file_ext, type)
     subdir = subdir_for(md5)
     file = file_name(md5, file_ext, type)