Addressing pixels of Unicorn Phat wierdness

From recollection, that shouldn’t be the case, but I’d have to look into it. To make things as compatible as possible with Unicorn HAT I chose to simply ignore any set_pixel calls that fall outside of the usable pHAT area, so a Unicorn HAT example can be run with just the set_layout call and not spew countless errors or abort immediately.