mscoree: fix an error in string access

[Rafał Mużyło]

mscoree: fix an error in string access

If parsed_config.private_path is an empty string, wine is doing a Bad
Thing. It shouldn't.

Signed-off-by: Rafał Mużyło

[Vincent Povirk (they/them)]

Thanks. Unfortunately, this doesn't seem to have been picked up by the
patch tracker.

I think we should treat an empty string the same as a NULL string and
not try to parse it at all.