moving: /do/ redraw the prior line when the viewport hasn't changed
Benno Schulenberg authored
The complementary test on current_y should only be done when doing
a scroll-only, because only then the prior line can be offscreen.

This fixes https://savannah.gnu.org/bugs/?50658

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Reported-by: default avatarDavid Lawrence Ramsey <pooka109@gmail.com>
bc876ca7