Fix panic caused by unsupported TIFF format

[DNEGEL3125]

TIFF sample format IEEEFP is currently not supported by image crate.

Returning an error instead of calling unwrap() allows Python code to catch it.

mitmproxy/tools/web/app.py:

try:
    # called `Result::unwrap()` on an `Err` value: Unsupported(UnsupportedError { format: Exact(Tiff), kind: GenericFeature("Unhandled TIFF sample format IEEEFP") })
    icon_bytes = mitmproxy_rs.process_info.executable_icon(path)
except Exception:
    icon_bytes = TRANSPARENT_PNG

[mhils]

Fantastic, thank you so much! 😃 🍰