fsrtl: fstub: Coverity defects fixes

Coverity fixes:

• CID 701341: Dereference before null check (ntoskrnl/fsrtl/filelock.c) -> it was certainly a check against LockInfo / FileLock>LockInformation, instead of on FileLock.
• CID 701288: Dereference null return value (ntoskrnl/fsrtl/filelock.c) --> add a check against Conflict just before its use.
• CID 716770: Unusued pointer value (ntoskrnl/fsrtl/filelock.c) --> Remove the unneeded RemadeElementInserted variable.

Also in ntoskrnl/fsrtl/filelock.c :

• Code formatting (easily localizable)
• Rename the already declared Find variable to LockElement (in the for-loop line 938)

• CID 701342: Dereference before null check (ntoskrnl/fsrtl/notify.c), concerning the NotifyChange variable. At this point, NotifyChange was allocated by a call to ExAllocatePoolWithTag (line 587) with the POOL_RAISE_IF_ALLOCATION_FAILURE flag. Therefore after the flag, the NotifyChange variable CANNOT be null.

• CID 716576/7/8: Resource leak + CID 514636: Dereference after null check + CID 716805: Use after free (ntoskrnl/fstub/disksup.c) --> applying patch from Thomas Faber
  Also, simplify ZwOpenKey + ZwCreateKey --> ZwCreateKey, since the latter open an existing key if any.

• CID 701302: Unintentional integer overflow (ntoskrnl/fstub/fstubex.c) --> cast to ULONGLONG

WARNING !!
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In ntoskrnl/fsrtl/fastio.c, largemcb.c -> some dead and/or "bizarre" code.