Fix UnboundLocalError on parentDir when connecting to Samba (Linux) shares

[ghecko]

Summary

When using any impacket-based tool (nxc, smbclient-ng, etc.) to connect to a
Samba/Linux SMB share, the connection fails with:

[error] cannot access local variable 'parentDir' where it is not associated with a value

This happens when the SMB server advertises dialect >= 3.0 with directory
leasing support, and the client accesses a file at the root of the share.

Root cause

In impacket/smb3.py, the SMB2_CREATE handler has an indentation bug in the
directory leasing logic (around line 1267-1277):

if len(fileName.split('\\')) > 2:
    parentDir = ntpath.dirname(pathName)
if parentDir in self.GlobalFileTable:   # <-- outside the guard!

parentDir is only assigned when the path has more than 2 components (i.e. not
at share root), but the code referencing it sits outside that if block. For
root-level paths (common on Samba shares) parentDir is never bound, causing
an UnboundLocalError.

Fix

Move the if parentDir in self.GlobalFileTable / else block inside the
if len(...) > 2: guard, so that parent directory lease tracking is only
attempted when a parent directory actually exists:

if len(fileName.split('\\')) > 2:
    parentDir = ntpath.dirname(pathName)
    if parentDir in self.GlobalFileTable:
        raise Exception("Don't know what to do now! :-o")
    else:
        parentEntry = copy.deepcopy(FILE)
        parentEntry['LeaseKey']   = uuid.generate()
        parentEntry['LeaseState'] = SMB2_LEASE_NONE
        self.GlobalFileTable[parentDir] = parentEntry

This matches the original intent described by the inline comment
"Is this file NOT on the root directory?".

Impact

Affects any impacket consumer connecting to Samba/Linux shares over SMB3 with
directory leasing enabled. Windows shares are less commonly affected because
paths tend to include subdirectories (e.g. C$\Windows\...).