Fix `paint_quad` behavior change which clamped corner rounding (#27472)

Turns out that git deletion indicator relied on using larger-than-bounds
corner rounding - see
https://github.com/zed-industries/zed/pull/27460#issuecomment-2753174153

Release Notes:

- N/A
e091c5faafMichael Sloan committed on 3/26/2025, 5:09:18 AM· committed by GitHubparent931a6d6
3 files changedLine totals unavailable