so by chance i discovered efreet is doing bad things(tm) when
expanding/appending to string buffers to generate commands based off
desktop files. the string append basically was buggy, so fixed it by
making it a lot simpler and more obvious and now reliable.
@fix
When doing efreet_desktop_command_append_multiple we add all files from
command, whilst still looping command->files. So the command was created
with all files for all files.
Set l to NULL, since we parse all elements in command->files in
efreet_desktop_command_append_multiple to break the loop.