First row of alt buffer is drawn incorrectly in some situations

[mofux]

Editing a file in mc and scrolling (either with scroll wheel or using the arrow keys) renders the first row of the screen incorrectly:

This bug was likely introduced by #855 and tried to fix by #923 without success. Note It does only happen on the v3 branch, not master.

To reproduce, install mc brew install mc, then in the demo mcedit lib/Terminal.js and scroll using the wheel or alt+down and alt+up

[mofux]

Trying to shed some light into this issue.

mcedit showing the file

Then pressing alt+down to scroll down one line in the file produces the following
screen update sequence from the TTY:

[39m[49m[2;23r[2;1H[1M[1;24r[1;35H[30m[46m2[6C2[9C4[14C32[5C0[23;1H[37m[44mimport { Buffer } from './Buffer';                                               [2;1H

which translates to:

// only use row 2-23 for scroll (`[2;23r`)
InputHandler.setScrollRegion(2,23)
// use full screen for scroll (`[1;24r`)
InputHandler.setScrollRegion(1,24)

and finally ends in this state: