BUG: REGR: read_csv with memory_map=True raises UnicodeDecodeError: 'utf-8' codec can't decode byte 0xc4 in position 262143: unexpected end of data 
- [x ] closes #43540 
- [x ] tests added / passed
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit) for how to run them
- [x ] whatsnew entry
