can't parse invalid utf8 in sequoia_openpgp_ffi::parse::pgp_packet_parser_from_bytes

fuzzing output:

thread '<unnamed>' panicked at 'byte index 11 is not a char boundary; it is inside '\u{318}' (bytes 10..12) of `-$z̘`', /home/capitol/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libcore/str/mod.rs:1987:47

unit test to reproduce:

#[test]
fn crash_on_invalid_text() {
    let data:[u8; 68] = [63, 9, 45, 10, 45, 10, 45, 45, 45, 45, 45, 66, 69, 71, 73, 78, 32, 80, 71, 80, 32, 77, 69, 83, 83, 65, 71, 69, 45, 45, 45, 45, 45, 45, 152, 152, 152, 152, 152, 152, 255, 29, 152, 152, 152, 152, 152, 152, 152, 152, 152, 152, 10, 91, 45, 10, 45, 14, 0, 36, 0, 0, 30, 122, 4, 2, 204, 152];

    let t = sequoia_openpgp_ffi::parse::pgp_packet_parser_from_bytes(core::option::Option::None, &data[0], data.len());

    println!("{:?}", t);
}