Service username is not displayed

[brettgus]

I've noticed that the username displays "None" when dumping sam/system/security using pypykatz registry.

After I remove decode('utf-16-le') in system.py it functions as intended:

I've only tested this with Windows 7, 10 and Windows 2022 so far. I will submit a PR for this.

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I've also noticed that pypykatz smb regdump works on Windows 7 but shows "None" for the service username on Windows 10/2022. It doesn't display the error, but it's: 'bytes' object has no attribute 'get_key_offsets' when it trys to call val = await self.hive.get_value(key) in asystem.py.