SDL: Fixed crash if SetMappingValue() is passed a NULL key

SDL Commits
1 
From 255f297439fdaeb8ba3e96fab123381b7b70bef2 Mon Sep 17 00:00:00 2001
From: Sam Lantinga <[EMAIL REDACTED]>
Date: Wed, 19 Jul 2023 09:23:08 -0700
Subject: [PATCH] Fixed crash if SetMappingValue() is passed a NULL key

---
 test/gamepadutils.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/test/gamepadutils.c b/test/gamepadutils.c
index 0661fe83e7aa..d90a540307ea 100644
--- a/test/gamepadutils.c
+++ b/test/gamepadutils.c
@@ -2463,6 +2463,10 @@ static char *SetMappingValue(char *mapping, const char *key, const char *value)
     char **new_values = NULL;
     SDL_bool result = SDL_FALSE;
 
+    if (!key) {
+        return mapping;
+    }
+
     SplitMapping(mapping, &parts);
     i = FindMappingKey(&parts, key);
     if (i >= 0) {