Filename encoding for external viewer inconsistent

From Malte Plath:

after finally configuring some external viewers for VM in NTEmacs,
I noticed that the encoding used for saving the temporary file and
that for calling the program to display it are not consistent. (Well,
it may be an inconsistency in Windows...)

The filename of the saved file was effectively windows-1252 (default
in German Windows XP) as you can see in the explorer window in the
screen shot. Apparently the viewer (IrfanView [i_view32.exe] in this
case) was called with a UTF-8 string, though.

The content description in the original mail was: | Content-Type: image/jpeg;
name*=ISO-8859-1''Verpuffende%20Fernw%E4rme.jpg | Content-Disposition:
attachment; filename*=ISO-8859-1''Verpuffende%20Fernw%E4rme.jpg |
Content-Transfer-Encoding: base64 The text part of the original mail was
encoded as UTF-8.

Attachment: Screenshot of image file in Explorer and error message of
viewer program.