If a theme cannot be found in the user directory, try in system
data dirs (XDG_DATA_DIRS, usually /usr/share and /usr/local/share)
Signed-off-by: Giovanni Campagna <gcampagna@src.gnome.org>
Previously null stylesheets were ignored, making it impossible to
reset the default. We still need to filter out invalid (non existing)
stylesheets, as no check is performed by shell code.
Martin Dengler
Elad Alfassa
Giovanni Campagna
John Stowers