Sometimes, the RPi fails to send out a message in time, leading
to two, back-to-back SPI transactions. The beginning of the second
is then lost in the long lcd_display() call. By applying this
patch, we now miss the incomplete frame entirely, but at least we
don't display garbage on the screen. Just looks like stutter.
The real solution would be to fix in on the Linux / Python side,
but this workaround is better than nothing for now.
