Fixed the grass rendering

[viktor-ferenczi]

Fixed the grass rendering (div by zero in shader).

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• Fixes the inverted grass LOD pattern in Space Engineers on the NVIDIA Vulkan driver (no grass near the player, grass beyond a sharp circular boundary), caused by undefined division-by-zero in shaders translated by DXVK's dxbc-spirv converter.
• Root cause: DXBC defines unsigned division by zero as returning all bits set, but Converter::handleIntDivide emitted SPIR-V OpUDiv/OpUMod with the original, possibly-zero divisor and only corrected the result with a later OpSelect. SPIR-V leaves the zero-divisor operation itself undefined, and the undefined result leaked into the foliage skip logic (GetSkip in Foliage.hlsl).
• Adds Patches/dxvk/0003-dxbc-spirv-select-nonzero-divisor.patch: selects a nonzero divisor (-1 when the divisor is zero) before emitting OpUDiv/OpUMod, keeping the existing result selection so DXBC semantics are unchanged while the SPIR-V is always defined.
• Adds the same fix re-rooted onto vkd3d-proton's own vendored copy of the converter (Patches/vkd3d-proton/vkd3d-proton-dxbc-spirv-select-nonzero-divisor.patch), so SM ≤ 5 DXBC shaders reaching the SE2 D3D12 layer are covered too.
• The fix lands in the shared DXBC converter rather than a game-shader or driver-specific workaround, so all DXBC shaders get defined division; both patches are documented in the series READMEs with provenance and should be dropped once upstream doitsujin/dxbc-spirv contains the fix and the pins catch up.
• Verified with the dxbc-spirv converter test suite (199,608 checks, no failures) and in-game before/after comparison; the patched DXVK build is reproducible and ships byte-identically in both the SE1 and SE2 archives.