kernel32: Implement GetVolumePathName.

[Dan Kegel]

Fails test here?

../../../tools/runtest -q -P wine -M ntdll.dll -T ../../.. -p
ntdll_test.exe.so file.c && touch file.ok
Unhandled exception: page fault on read access to 0x00212b18 in 32-bit
code (0x7bc47995).
Backtrace:
=>0 HEAP_CreateFreeBlock+0xbb(subheap=0x110014, ptr=0x122b48,
size=0xeffd0) [dlls/ntdll/heap.c:583]
  1 HEAP_ShrinkBlock+0x42(subheap=0x110014, pArena=0x122b08,
size=0x38) [dlls/ntdll/heap.c:685]
  2 RtlAllocateHeap+0x2a8(heap=0x110000, flags=0x2, size=0x38)
[dlls/ntdll/heap.c:1699]
  3 RtlDosPathNameToNtPathName_U+0x35c(dos_path="C:\windows\system32",
ntpath=0x32fbb4, file_part=(nil), cd=(nil)) [dlls/ntdll/path.c:394]
  4 GetVolumePathNameW+0x107(filename="C:\windows\system32",
volumepathname="?Ir\sandbox\slave\(", buflen=0x14)
[dlls/kernel32/volume.c:1767]
  5 test_file_name_information+0x179() [dlls/ntdll/tests/file.c:1304]
  6 func_file+0x374() [dlls/ntdll/tests/file.c:1726]
  7 run_test+0x9e(name="file.c") [include/wine/test.h:556]
  8 main+0x23a(argc=<?>, argv=0x1103c8) [include/wine/test.h:624]
0x7bc47995 HEAP_CreateFreeBlock+0xbb [dlls/ntdll/heap.c:583] in ntdll:
movl     0x0(%eax),%eax
583             (*(DWORD *)((char *)ptr + size) & ARENA_FLAG_FREE))