WPrefs: fix conversion of old "Apercu" setting to the new keywords
As pointed by Josip, the code for loading the legacy setting keywords for
the Minipreview feature did not update correctly the configuration:
- if the setting used a size as a multiple of icon size, this was
understood as the minimum pixel size, which meant here disabling the
feature. The code is now consistent with what Window Maker does;
- if the old keyword were found, they were loaded but not removed from the
database after creating the new ones, which is a source of problem as
Window Maker assumes that the presence of the legacy keywords means they
are to be taken in consideration.
Reported-by: Josip Deanovic <djosip+news@linuxpages.net>
Signed-off-by: Christophe CURIS <christophe.curis@free.fr>