Fix set-face-attribute error

Currently, the value of nethack-map-tile-face causes an error on Emacs 24.3.1 because ":name" is not in defface's ATTS property list:

**Error message:**
```
set-face-attribute: Font not available: #<font-spec nil nil 6x10 nil nil nil nil
nil nil nil nil nil ((:name . "6x10") (user-spec . "6x10"))>
```

**M-x emacs-version:**
```
GNU Emacs 24.3.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.8.1) of 2013-04-30 on eric
```

Please tell me if this is a stupid solution, I can only confirm that it works for me.  Without this change it only runs after invoking M-x nethack three times (I don't know what sorcery is at work there).