f39680de45
WeCom's CDN returns `content-type: application/octet-stream` for images. `mimetypes.guess_extension` maps that to ".bin", a truthy value that short-circuited `_guess_extension()` before the magic-byte detector ran, so every inbound image was cached as `img_*.bin`. Treat ".bin" as "unknown" so the URL suffix / magic-byte fallback decides. The second half of the report (URL-encoded, unpadded `aeskey`) is already handled on main by `_decrypt_file_bytes`. Salvage of PR #10187 by @nightq onto `plugins/platforms/wecom/media.py`. Fixes #10085