swift234

[CodeCompletion] Fix crash completing method with associated type

    protocol P { typealias T; func foo() -> T }
    func invalid(x: P) { x.#^COMPLETE^#

We were trying to access a null Type created because the associated type
doesn't make sense in the protocol type P (we can only use P as a
generic constraint, but it shouldn't crash code completion if we use it
incorrectly).

For rdar://problem/20305938

Swift SVN r28588