Incorrect results when using "Show items from unimported namespaces" to complete generic types

**Steps to Reproduce**:

I was trying to complete System.Collections.Generics.List<T>, but I got the non-generic version of this type:

![TypeCompletionForGenerics](https://user-images.githubusercontent.com/1103906/60062863-3d140700-973e-11e9-9df7-4f7c445121bf.gif)


**Expected Behavior**:
`List<T>` to be committed.

**Actual Behavior**:
List was committed.
