Add missing null check pointer in imgui_impl_glfw.cpp - ImGui_ImplGlfw_DestroyWindow

[AMS21]

Been experimenting a bit with my application which uses ImGui with GLFW and OpenGL3 as its backend. Sometimes when closing the application I notices the following output:

/mnt/data/dev/DLXEmu/external/imgui/backends/imgui_impl_glfw.cpp:703:25: runtime error: member access within null pointer of type 'ImGui_ImplGlfw_Data'
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /mnt/data/dev/DLXEmu/external/imgui/backends/imgui_impl_glfw.cpp:703:25 in

Look like the function is trying to deference a null pointer, which this patch should prevent.

[ocornut]

You must be doing wrong, as ImGui_ImplGlfw_DestroyWindow() shouldn't be called after the backend is shutdown.

The examples are calling shutdown on Renderer backend and then on Platform backend.
Either generally call ImGui::DestroyPlatformWindows()
Which backends are you using and what are your shutdown call order?

[ocornut]

So:
With default GLFW, SDL, Win32 backends, with multi-viewport enabled, until now it was assumed and required that you Shutdown the Renderer backend BEFORE the Platform backend (the opposite of Initialization)

I somehow relaxed this with a patch now (bac748f) but this is not officially supported.
Best to shutdown in the correct order.

[AMS21]

Ah, thanks for clarifying. You are correct I was accidentally doing it in the wrong order. Then I would suggest adding an assertion statement like this:

static void ImGui_ImplGlfw_DestroyWindow(ImGuiViewport* viewport)
{
    ImGui_ImplGlfw_Data* bd = ImGui_ImplGlfw_GetBackendData();
    IM_ASSERT(bd != NULL && "No platform backend to shutdown, or already shutdown. Did you shutdown in the correct order? Note that you need to shutdown the Renderer BEFORE the Platform backend (the opposite of Initialization)");

    if (ImGui_ImplGlfw_ViewportData* vd = (ImGui_ImplGlfw_ViewportData*)viewport->PlatformUserData)
    {
    (...)
}