wl-mime.el (wl-mime-save-content): Fix incorrect usage of `read-file-name'.

wl-mime.el (wl-mime-save-content): Fix incorrect usage of `read-file-name'.

* wl-mime.el (wl-mime-save-content): Fix incorrect usage of
`read-file-name'.

Function signature is

(read-file-name PROMPT &optional DIR DEFAULT-FILENAME MUSTMATCH INITIAL PREDICATE)

Passing the full path to the target file as second argument causes
problems with saving attachments when `ido-mode' is enabled. The
function signature didn't change in 22 and as it seems didn't change
in 21 (guessing from the usage, couldn't compile 21 on x64 system).