SDL: Initialize the padding of aligned allocations to zero (341f9)

SDL Commits
1 
From 341f9108352192141f16cc5b35cd8f971508dbff Mon Sep 17 00:00:00 2001
From: Sam Lantinga <[EMAIL REDACTED]>
Date: Wed, 12 Mar 2025 11:42:02 -0700
Subject: [PATCH] Initialize the padding of aligned allocations to zero

Fixes valgrind uninitialized memory errors when doing SIMD blits
e.g. testautomation --filter surface_testScale

(cherry picked from commit 3235a4eb4fdb9080f946ed28e9a7f75506272e61)
---
 src/stdlib/SDL_stdlib.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/stdlib/SDL_stdlib.c b/src/stdlib/SDL_stdlib.c
index 98faab95a35e3..093b2bec47903 100644
--- a/src/stdlib/SDL_stdlib.c
+++ b/src/stdlib/SDL_stdlib.c
@@ -533,6 +533,7 @@ void *SDL_aligned_alloc(size_t alignment, size_t size)
 {
     size_t padding;
     Uint8 *result = NULL;
+    size_t requested_size = size;
 
     if (alignment < sizeof(void*)) {
         alignment = sizeof(void*);
@@ -552,6 +553,11 @@ void *SDL_aligned_alloc(size_t alignment, size_t size)
 
             // Store the original pointer right before the returned value
             SDL_memcpy(result - sizeof(original), &original, sizeof(original));
+
+            // Initialize the padding to zero
+            if (padding > 0) {
+                SDL_memset(result + requested_size, 0, padding);
+            }
         }
     }
     return result;