Fix leak of 'fname' introduced by the rewrite of write_random_seed in

[sgt/putty] / windows / website.url

[InternetShortcut]
URL=http://www.chiark.greenend.org.uk/~sgtatham/putty/
\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0