Read packed three-byte vertex attributes without touching the next word

load_u24 and raw_fetch_u8_3 read a whole 32-bit word pair even when the
three bytes sit in the first word, so an attribute at the end of its
binding read past it. Release builds disable Dawn's robustness, so that
read isn't clamped.

From upstream patchzyy/Wiicompiled 6f14bde (#244, KartPad 0f6b274).

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Wg7mB8ogCWmp9GH19Uc82B

aurora-main/lib/gx/shader.cpp

@@ -1739,8 +1739,22 @@ fn load_u16(p: ptr<storage, array<u32>>, byte_off: u32, le: bool) -> u32 {{
   return bswap16(raw, le);
 }}
 
+fn load_u24_raw(p: ptr<storage, array<u32>>, byte_off: u32) -> u32 {{
+  let word_idx = byte_off >> 2u;
+  let sub = byte_off & 3u;
+  let word = p[word_idx];
+  // Three bytes at offsets zero or one fit entirely in this word. Do not
+  // access the next word: this attribute may end at the binding boundary.
+  if (sub <= 1u) {{
+    return (word >> (sub * 8u)) & 0x00FFFFFFu;
+  }}
+  let next = p[word_idx + 1u];
+  let shift = sub * 8u;
+  return ((word >> shift) | (next << (32u - shift))) & 0x00FFFFFFu;
+}}
+
 fn load_u24(p: ptr<storage, array<u32>>, byte_off: u32, le: bool) -> u32 {{
-  let raw = load_u32_raw(p, byte_off) & 0x00FFFFFFu;
+  let raw = load_u24_raw(p, byte_off);
   if (le) {{
     return raw;
   }}
@@ -1780,7 +1794,7 @@ fn raw_fetch_u8_2(p: ptr<storage, array<u32>>, byte_off: u32) -> vec2u {{
 }}
 
 fn raw_fetch_u8_3(p: ptr<storage, array<u32>>, byte_off: u32) -> vec3u {{
-  let raw = load_u32_raw(p, byte_off);
+  let raw = load_u24_raw(p, byte_off);
   return vec3u(
     extractBits(raw, 0u, 8u),
     extractBits(raw, 8u, 8u),