ntdll: fix memory leak in GetDiskFreeSpaceW

[Dan Kegel]

Found while valgrinding chromium's app_unittests.

Leak stack was
2,080 bytes in 4 blocks are definitely lost in loss record 1,376 of 1,451
   at RtlAllocateHeap (heap.c:1423)
   by get_full_path_helper (path.c:643)
   by RtlGetFullPathName_U (path.c:798)
   by RtlDosPathNameToNtPathName_U (path.c:379)
   by open_device_root (volume.c:160)
   by GetDiskFreeSpaceW (volume.c:1480)
-------------- next part --------------
A non-text attachment was scrubbed...
Name: leak.patch
Type: text/x-patch
Size: 1343 bytes
Desc: not available
URL: <http://www.winehq.org/pipermail/wine-patches/attachments/20091109/55346258/attachment.bin>