Better fix for static analysis issue in SDL_DestroyRenderer().

Follow up fix for Bugzilla #3544.

src/render/SDL_render.c

@@ -1938,7 +1938,9 @@ SDL_DestroyRenderer(SDL_Renderer * renderer)
 
     /* Free existing textures for this renderer */
     while (renderer->textures) {
+        SDL_Texture *tex = renderer->textures;
         SDL_DestroyTexture(renderer->textures);
+        SDL_assert(tex != renderer->textures);  /* satisfy static analysis. */
     }
 
     if (renderer->window) {