This patch fixes GetDiskFreeSpaceA/W when an NT-style GUID volume path is
provided e.g. "\\?\Volume{00000000-0000-0000-0000-000000000043}\" as might be
retrieved by FindFirstVolumeA/W and FindNextVolumeA/W.

Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=53547Signed-off-by: Joel Holdsworth <joel@airwebreathe.org.uk>