Generated source is missing namespaces

[jhartmann123]

Situation:
We have an extension method that cannot be found in the generated source, as the namespace of it does not get imported.

It looks like that namespaces do not get imported, if "children" of it are already present.

Tested with versions 2.3.0 and 3.0.0-beta.1

Repro: Projectables.ExtensionMethod.zip

Projectables.ExtensionMethod.Foo.ResultExtensions contains a [Projectable]-Method, which uses two extension methods:

• ConvertToTwo() is defined in the namespace Projectables.ExtensionMethod
• ConvertToThree() is defined in the namespace Projectables.ExtensionMethod.Extensions

While Projectables.ExtensionMethod.Extensions does get imported in the generated source, Projectables.ExtensionMethod does not, resulting in the error