First image update after power off starting with undefined frame buffer

[RobPo]

For updating, the ePaper waveform also needs to know the actual image content in order to chose the correct waveform transition. This is handled by the driver IC, but not working for the very first image update after power cycling. Although the driven image looks more or less OK the media is driven imbalanced and the overall contrast id degraded. Workaround is to first drive an (invisible) nullframe update after each initialisation.