Open file bug with .wld files

[Sambo]

This isn't anything major, but when selecting the file type to open, SMBX world files are set to *.wldx instead of *.wld. And the icon that used to be on the file with the little globe is gone. Now it just uses the same icon as .lvl files.

[Wohlstand]

This is a little mistake in the installer, I will fix it. If you have those mistakes with associations, simply open [Tools -> "Application settings"] and press "Associate file extensions" to re-associate them correctly