3.1 Runtime prompt fails if .NET Core 2.x runtime is installed

[Symbai]

With .NET Core 3.1 the apphost now prompts on missing .NET Core runtime which is amazing. Sadly the application still silently crashes in the following scenario:

• .NET Framework 4.7 or higher installed
• .NET Core 2.1 Runtime installed

In such a scenario no prompt is shown, not even an entry in the event viewer. It might be caused by the core runtime is installed but the "desktop" stuff is not. However there should be definitely a prompt.

Demo:

Related #3816 and #3761
ping @dagood @elinor-fung