stubgen crash when a referenced module is a DLL

[Avasam]

Crash Report
Same as #13822 (#13822 (comment)), but for stubgen. I've just tried it out in 0.990
stubgen crashes when a referenced module is a DLL, as it seemingly tries to parse the .dll's content as text.

Traceback

PS C:\Users\Avasam\Documents\Git\typeshed> stubgen -p pywintypes
Critical error during semantic analysis: mypy: can't decode file 'C:\Users\Avasam\Documents\Git\typeshed\.venv\Lib\site-packages\pywin32_system32\pywintypes39.dll': 'utf-8' codec can't decode byte 0x90 in position 2: invalid start byte

To Reproduce
pip install pywin32
stubgen -p pywintypes

Your Environment

• Mypy version used: 0.990 (compiled: yes)
• Mypy command-line flags: (see above)
• Mypy configuration options from mypy.ini (and other config files): (see above)
• Python version used: 3.9.13
• Operating system and version: Windows 10.0.19044 Build 19044

[hauntsaninja]

Thanks, want to make a PR? :-)

[Avasam]

Given how simple the fix you did for stubtest was, sure, I can try it out.