lcd.drawLine(...) gives wrong result on X7

[floaledm]

This is a followup to #4464
There's still an issue on X7 with drawLine(x1,y1,x2,y2,...) when x1>x2, e.g.:

is the output of this code:
lcd.drawLine(10,10,10,20, SOLID, 0)
lcd.drawLine(10,10,20,10, SOLID, 0)
lcd.drawLine(30,40,30,30, SOLID, 0)
lcd.drawLine(40,30,30,30, SOLID, 0) -> this is the line that fails to draw properly