PlusGUI.py fails converting Windows 98 Plus! theme

When I tried installing the Windows 98 Jungle theme with `../PlusGUI.py ../Jungle/Jungle.theme`, PlusGUI.py failed with

```
Traceback (most recent call last):
File "/home/user/src/Chicago95/Plus/tmp/../PlusGUI.py", line 1207, in install_accept
self.install_theme()
File "/home/user/src/Chicago95/Plus/tmp/../PlusGUI.py", line 1232, in install_theme
self.theme.go(cursors=self.install_cursors, icons=self.install_icons, wallpaper=self.install_wallpaper,
File "/home/user/src/Chicago95/Plus/pluslib.py", line 155, in go
self.generate_theme(cursors, icons, wallpaper, sounds, colors, fonts, screensaver)
File "/home/user/src/Chicago95/Plus/pluslib.py", line 274, in generate_theme
self.convert_colors()
File "/home/user/src/Chicago95/Plus/pluslib.py", line 1261, in convert_colors
self.theme_config['colors']['buttondkshadow']['color'],
KeyError: 'buttondkshadow'
```