maximized() used to align the image with (0,0) so that it is shifted to the right or bottom. Most wallpapers are designed from the center, so this behavior is not desired usually. With this commit the wallpaper is centered when no offset is set. To get the old behavior use {x=0, y=0} for the offset parameter.
When no wallpaper exists yet, instead of creating a black image surface which
covers all the screens, just create a surface for the screen which we need. This
means that way less pixels have to be uploaded to the X11 server, which should
be faster.
Signed-off-by: Uli Schlachter <psychon@znc.in>