Win: Fix compilation error on Windows (xgl_helper.py).

Win: Fix compilation error on Windows (xgl_helper.py).

Visual Studio doesn't like the following code construct:

    if (<some test>)
        return <something>;
    <type> variable [= <intial-value>];

We have to use curly-braces, as in:

    if (<some test>) {
        return <something>;
    }
    <type> variable [= <intial-value>];