Fix jpeg save quality

I got extremely bad quality when editing and saving JPEGs, and
apparently didn't it only not initialize the quality when saving it also
stored random garbage values in the config files, so they were preserved
forever.

So fetch the current value from config initially, and fetch it again
when calling save as, in case it changed. Still a bit broken, it won't
be reloaded if just saving and it is changed elsewhere, but this is the
minimal change that seems to fix the current implementation.

Reviewed By: ngraham

Differential Revision: https://phabricator.kde.org/D28348