backends/drm: restrict damage area to the screen's size

Vlad Zahorodniirequested to merge
work/cherry-pick-de12db73 into Plasma/6.2

Scissor rectangles going outside of the framebuffer cause OpenGL warnings

BUG: 492152

(cherry picked from commit de12db73)

Co-authored-by: Xaver Hugl xaver.hugl@gmail.com

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