Issue Description:

Let's say I have the following function:

func foo<T>(_ closure: ((T) -> Void) -> Void) {
    print(type(of: T.self)) 
}

Calling the following infers the proper type for T, String:

foo { bar in
    bar("Hello")
}
// Prints "String.Type"

The problem arises when bar is called an additional time within the closure:

foo { bar in  // Error: Generic parameter 'T' could not be inferred
    bar("Hello")
    bar("World")
}

The only way this issue can be worked around, is by explicitly specifying the type of `bar`:

foo { (bar: (String) -> Void) in
    bar("Hello")
    bar("World")
}
// Prints "String.Type"

It seems to me that if Swift can infer the type for the single invocation case, it ought to be able to infer the type for the case with multiple invocations.