SDL_shadercross: Fix segfault when defines is NULL

SDL Commits
1 
From 864b6fbdc97ea21ac0c98265182c6bfae1efcbeb Mon Sep 17 00:00:00 2001
From: cosmonaut <[EMAIL REDACTED]>
Date: Thu, 19 Dec 2024 14:39:43 -0800
Subject: [PATCH] Fix segfault when defines is NULL

---
 src/SDL_shadercross.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/src/SDL_shadercross.c b/src/SDL_shadercross.c
index 32db3e8..16df52c 100644
--- a/src/SDL_shadercross.c
+++ b/src/SDL_shadercross.c
@@ -409,11 +409,13 @@ static void *SDL_ShaderCross_INTERNAL_CompileUsingDXC(
         return NULL;
     }
 
-    for (Uint32 i = 0; i < MAX_DEFINES; i += 1) {
-        if (info->defines[i].name == NULL) {
-            break;
+    if (info->defines != NULL) {
+        for (Uint32 i = 0; i < MAX_DEFINES; i += 1) {
+            if (info->defines[i].name == NULL) {
+                break;
+            }
+            numDefineStrings += 1;
         }
-        numDefineStrings += 1;
     }
 
     char defineString[MAX_DEFINE_STRING_LENGTH];