Made error handling more consistent in D3D12_RenderReadPixels()

(cherry picked from commit 90262f274ab73a2a0db227f8a1a3ea823ba0faec)

src/render/direct3d12/SDL_render_d3d12.c

@@ -2837,8 +2837,8 @@ static int D3D12_RenderReadPixels(SDL_Renderer *renderer, const SDL_Rect *rect,
                       NULL,
                       (void **)&textureMemory);
     if (FAILED(result)) {
-        SAFE_RELEASE(readbackBuffer);
-        return WIN_SetErrorFromHRESULT(SDL_COMPOSE_ERROR("ID3D12Resource::Map [map staging texture]"), result);
+        WIN_SetErrorFromHRESULT(SDL_COMPOSE_ERROR("ID3D12Resource::Map [map staging texture]"), result);
+        goto done;
     }
 
     /* Copy the data into the desired buffer, converting pixels to the