win: Fix default path for native dialogs

- Call SetFolder instead of SetDefaultFolder on the dialog to set the default path. 

MSDN documentation states that SetDefaultFolder "Sets the folder used as a default if there is not a recently used folder value available."

http://msdn.microsoft.com/en-us/library/windows/desktop/bb775972(v=vs.85).aspx

MSDN documentation states that SetFolder "Sets a folder that is always selected when the dialog is opened, regardless of previous user action."

http://msdn.microsoft.com/en-us/library/windows/desktop/bb761828(v=vs.85).aspx