SDL: GPU: Fix another OpenXR zero-length copy

SDL Commits
1 
From c1aa9f43fad2694fc903c4c96c06d8e80cedfd95 Mon Sep 17 00:00:00 2001
From: Evan Hemsley <[EMAIL REDACTED]>
Date: Mon, 3 Aug 2026 14:16:13 -0700
Subject: [PATCH] GPU: Fix another OpenXR zero-length copy

---
 src/gpu/xr/SDL_gpu_openxr.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/gpu/xr/SDL_gpu_openxr.c b/src/gpu/xr/SDL_gpu_openxr.c
index 1404f1260c6a8..e4104365d18cc 100644
--- a/src/gpu/xr/SDL_gpu_openxr.c
+++ b/src/gpu/xr/SDL_gpu_openxr.c
@@ -128,7 +128,9 @@ XrResult SDL_OPENXR_INTERNAL_GPUInitOpenXR(
 #endif
 
     const char **extensionNames = SDL_stack_alloc(const char *, userExtensionCount + platformExtensionCount);
-    SDL_memcpy((void *)extensionNames, userExtensionNames, sizeof(const char *) * (userExtensionCount));
+    if (userExtensionCount > 0) {
+        SDL_memcpy((void *)extensionNames, userExtensionNames, sizeof(const char *) * userExtensionCount);
+    }
     extensionNames[userExtensionCount] = gpuExtension.extensionName;
 #ifdef SDL_PLATFORM_ANDROID
     extensionNames[userExtensionCount + 1] = XR_KHR_ANDROID_CREATE_INSTANCE_EXTENSION_NAME;