Add a return parameter to ImGui_Impl...._NewFrame()

Why does CreateDeviceObjects return a bool if the NewFrame doesn't ?
Added the return parameter cause CreateDeviceObjects can fail.
It did fail on DX11 with feature level to 9.

ImGui/impls/windows/imgui_impl_dx12.cpp

@@ -668,8 +668,10 @@ void ImGui_ImplDX12_Shutdown()
     g_frameIndex = UINT_MAX;
 }
 
-void ImGui_ImplDX12_NewFrame()
+bool ImGui_ImplDX12_NewFrame()
 {
     if (!g_pPipelineState)
-        ImGui_ImplDX12_CreateDeviceObjects();
+        return ImGui_ImplDX12_CreateDeviceObjects();
+
+    return true;
 }