Don't immediately throw in ConstructorInjectionConvention

[TheConstructor]

rather let the ModelFactory throw as the convention is applied twice in hosting case.

It took me some time to discover why the unit-test of my pull-request #178 started failing. I immediately suspected #175, but it took me an hour to realize that the convention is immediately applied when added to the builder. Worse: in CommandLineService it is applied twice!

_application.Conventions
    .UseDefaultConventions() // this will apply ConstructorInjectionConvention and throw
    .UseConstructorInjection(serviceProvider); // this would work

By setting the ModelFactory to a throw-implementation we get to the second invocation were we set up the real deal. Effect for other apps is that the exceptions are a bit later, but also less nested. This also gives room for other conventions to set-up ModelFactories.

[TheConstructor]

@natemcmaster I will probably only be able to fix the test after work. Was to keen on previewing #182 it seems :(

But it seems I manged to move the commit to be only included in #182.

[TheConstructor]

Everything should be ok now. Please @natemcmaster consider this pull-request. To be able to use constructor-injection with host-services after #175 either something like this is required or CommandLineService needs to be rewritten, so that UseConstructorInjection() is not called through UseDefaultConventions() or Application.AdditionalServices is initialized earlier.

[natemcmaster]

Thanks for fixing this!

[TheConstructor]

You're welcome! I am glad that we had/have a test!