text: Title: When sys.argv be changed, pudb3 cannot enter REPL
  Body: **Describe the bug**
  When sys.argv be changed, pudb3 cannot enter REPL
  
  **To Reproduce**
  test.py
  ```python
  import sys
  argv = sys.argv
  sys.argv = []
  print(1)
  print(2)
  print(3)
  sys.argv = argv
  print(4)
  print(5)
  print(6)
  ```
  
  `pudb3 test.py`, when `sys.argv` is `[]`, press `!` cannot enter REPL. when `sys.argv` recovery, press `!` can enter REPL.
  
  **Expected behavior**
  press `!` can enter REPL.
  
  **Additional context**
  Can we backup `sys.argv` when the program start, And when we press `!` recover `sys.argv` temporarily to avoid this bug?
  
  ## Complete:
  
  if some module of `sys.modules` (e.g, argparse) be changed, the same phenomenon will also happen.