When attempting to update cached payload sizes which utilize the
Rex::Powershell functionality, the BRE block which appropriates
initial code is called with the 'code' variable being a nil which
results in:
```
lib/rex/powershell/script.rb:40:in `initialize': no implicit
conversion of nil into String (TypeError)
```
This throws a conditional into the File.open call which presents an
empty string instead of a nil. This still results in the rescue
block having to catch the exception, but manages to keep the
payload size updating script happy an retains consistent
behavior.
HD Moore