Fixed that viewing the history of a wiki page with attachments raises an error (#12801).

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@11157 e93f8b46-1217-0410-a6f0-8f06a7374b81
Code cleanup (#12801).

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@11158 e93f8b46-1217-0410-a6f0-8f06a7374b81