Retrieve filenames of thumbnails when rendering a PDF (#35683).

Patch by Jens Krämer.

git-svn-id: http://svn.redmine.org/redmine/trunk@21212 e93f8b46-1217-0410-a6f0-8f06a7374b81

lib/redmine/export/pdf.rb

@@ -104,6 +104,10 @@ module Redmine
           atta = RDMPdfEncoding.attach(@attachments, attrname, "UTF-8")
           if atta
             return atta.diskfile
+          elsif %r{/attachments/thumbnail/(?<id>[^/]+)/(?<size>\d+)} =~ attrname and
+                atta = @attachments.find{|a| a.id.to_s == id} and
+                atta.readable? and atta.visible?
+            return atta.thumbnail(size: size)
           else
             return nil
           end