Pagedn skipping lines if editing-window resized

[dextarr]

Dear support,

I've found a pageup-down misbehavior in case the mcedit window is resized

create a test file
for i in $(seq 1 8); do echo $i>>test.file; done

steps to reproduce:

• open the file in mcedit (the cursor is on the first line)
• resize the editor window by clicking "*" in the upper right corner to display only 3 lines
• pressing pagedown results the window showing lines 5-7: skipping line 4
• pageup also doesnt work and skips line 4
• i expect the see line 4 during pagedown-up scrolling
• without resizing the window in step 2 pagedown-up works as intended

please consider fixing it,

thank you!

[zaytsev]

Relates to #4618 .