* backend/umax*: bugfixes:
* bugfix for DOR:
- bottom-right edge keeps in position if possible when DOR is switched on
* bugfix for Astra 610S color mode:
- scale_y is set to 0.5 if y_resolutions is smaller than optical_res/2
this does fix the color scan problems for Astra 610S.
Not tested for Astra 600S.