text: Title: Empty completion list for file in `aws s3 cp`
  Body: Typing on Debian:
  
  ```xsh
  pip install awscli
  
  $XONSH_TRACE_COMPLETIONS=True
  aws s3 cp <press tab to insert filename> s3://path/
  ```
  
  Result
  
  <img width="139" alt="Image" src="https://github.com/user-attachments/assets/411ccc3e-492e-43c1-af1a-8315e97f5e3d" />
  
  Trace (one result with empty space `' '`):
  ```xsh
  TRACE COMPLETIONS: Getting completions with context:
  TRACE COMPLETIONS: Got 1 results from exclusive completer 'bash':
  CompletionContext(command=CommandContext(args=(CommandArg(value='aws', opening_quote='', closing_quote='', is_io_redir=False), CommandArg(value='s3', opening_quote='', closing_quote='', is_io_redir=False), CommandArg(value='cp', opening_quote='', closing_quote='', is_io_redir=False), CommandArg(value='s3://path/', opening_quote='', closing_quote='', is_io_redir=False)), arg_index=3, prefix='track', suffix='', opening_quote='', closing_quote='', is_after_closing_quote=False, subcmd_opening=''), python=PythonContext('aws s3 cp track s3://path/', 15, is_sub_expression=False))
  [(RichCompletion(' ', prefix_len=5, append_closing_quote=False, append_space=True),
    5)]
  ```
  
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