Issue Description:

Given a throwing function, e.g.:

    func toss() throws -> Int {
        return 123
    }

Calling it using try? and handling the resulting optional using the ?? operator will not resolve to a non-optional:

let n: Int = try? toss() ?? 999

…instead giving the error message

Value of optional type 'Int?' not unwrapped; did you mean to use 'try!' or chain with '?'?

…as well as a fixit to replace try? with try!.

In Xcode, the function name will also not be highlighted as a function name until you apply the fixit, turning "try?" into "try!".

Wrapping the call in parentheses, e.g.:

let n: Int = (try? toss()) ?? 999

…the code will highlight and compile, but the expression should be solvable without.