Clarified that the contents of new textures aren't defined.

include/SDL3/SDL_render.h

@@ -479,6 +479,8 @@ extern SDL_DECLSPEC SDL_bool SDLCALL SDL_GetCurrentRenderOutputSize(SDL_Renderer
 /**
  * Create a texture for a rendering context.
  *
+ * The contents of a texture when first created are not defined.
+ *
  * \param renderer the rendering context.
  * \param format one of the enumerated values in SDL_PixelFormat.
  * \param access one of the enumerated values in SDL_TextureAccess.