effects/zoom: Fix crash on X11

On X11, the painted screen is meaningless, so the zoom effect doesn't
use it to store offscreen data. It can create problems when iterating
over offscreen data map.

The painted screen can't be used to determine the necessary offscreen
texture size too. X11 requires some special care.

This change adds explicit wayland checks.

BUG: 466376
(cherry picked from commit 1854224c)