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_dx10.cpp

@@ -548,8 +548,10 @@ void ImGui_ImplDX10_Shutdown()
     if (g_pd3dDevice) { g_pd3dDevice->Release(); g_pd3dDevice = NULL; }
 }
 
-void ImGui_ImplDX10_NewFrame()
+bool ImGui_ImplDX10_NewFrame()
 {
     if (!g_pFontSampler)
-        ImGui_ImplDX10_CreateDeviceObjects();
+        return ImGui_ImplDX10_CreateDeviceObjects();
+
+    return true;
 }