fix for very minor issue with advmame*x
|Reported by:||SF/lord_nightmare||Owned by:||fingolfin|
this fixes an extremely minor issue with advmame2x and advmame3x, regarding the left screen edge not correctly assuming that all offscreen pixels are black, which happens on all three other edges. so this fixes it.
Ticket imported from: #738563. Ticket imported from: patches/329.