[DISK]: Small fixes:

[DISK]: Small fixes:
- Check for malformed disk identifier, which must be at least 9 WCHARs long (as done by disk_new);
- Prevent possible memory leaks (missing ExFreePool's) + closing registry key.
Investigated by Lesan Ilie during tests; as part of CORE-13131.
- Make one of our hacks more readable (by me).
(We also note that this driver uses the ExAllocate/FreePool functions in the old-school way).

svn path=/trunk/; revision=74509