SDL: testaudio: Don't crash if renderer is NULL (happens during shutdown).

From b17151eb16e18354adc2412afb9c451f903188f5 Mon Sep 17 00:00:00 2001
From: "Ryan C. Gordon" <[EMAIL REDACTED]>
Date: Sat, 14 Oct 2023 13:43:22 -0400
Subject: [PATCH] testaudio: Don't crash if renderer is NULL (happens during
 shutdown).

---
 test/testaudio.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/test/testaudio.c b/test/testaudio.c
index 3cb71a764273..1508098f2191 100644
--- a/test/testaudio.c
+++ b/test/testaudio.c
@@ -416,11 +416,13 @@ static void DrawThings(SDL_Renderer *renderer)
 static void Draw(void)
 {
     SDL_Renderer *renderer = state->renderers[0];
-    SDL_SetRenderDrawBlendMode(renderer, SDL_BLENDMODE_BLEND);
-    SDL_SetRenderDrawColor(renderer, 64, 0, 64, 255);
-    SDL_RenderClear(renderer);
-    DrawThings(renderer);
-    SDL_RenderPresent(renderer);
+    if (renderer) {  /* might be NULL if we're shutting down. */
+        SDL_SetRenderDrawBlendMode(renderer, SDL_BLENDMODE_BLEND);
+        SDL_SetRenderDrawColor(renderer, 64, 0, 64, 255);
+        SDL_RenderClear(renderer);
+        DrawThings(renderer);
+        SDL_RenderPresent(renderer);
+    }
 }
 
 static void RepositionRowOfThings(const ThingType what, const float y)