Drawing Tool: encoding problems when using chinese fonts

Reported via mail:

Hi,

I find that, when editing an image, after I select a font with Chinese
name, the name displaying at the bottom becomes corrupted. Here's a
screenshot:
http://dimg.vim-cn.com/9f/1204db558c7a22dec6d89fe7673e06096c1221 . And
if you want to try, you may use the wqy-zenhei font with
LANG=zn_CN.UTF-8.

This happens because after the name from FontDescription-_to_string is
in some incorrect encoding. DrawingTool.pm can avoid these to_string
calls as in my patch.