Fix infinite loop caused by invalid UTF-8 bytes #2326

Job	Run time
cargo clippy	37s
codegen	35s
cargo bench	1m 15s
cargo +stable build	1m 11s
cargo +1.36 build (futures-{core, io, sink})	4m 16s
cargo +beta build	1m 3s
cargo doc	33s
cargo +nightly build	1m 12s
cargo hack check --feature-powerset	27s
cargo fmt	10s
cargo minimal-versions build	39s
cargo build --target thumbv7m-none-eabi	28s
cargo miri test	13m 18s
cargo test -Z sanitizer=address	5m 33s
cargo build --target thumbv6m-none-eabi	29s
cargo test -Z sanitizer=memory	3m 27s
cargo test (ubuntu-latest)	5m 28s
cargo test -Z sanitizer=thread	3m 17s
cargo test (macos-latest)	4m 33s
cargo +1.56 build	2m 29s
cargo test (windows-latest)	8m 26s
cargo test (ubuntu-latest, aarch64-unknown-linux-gnu)	5m 30s
cargo test (ubuntu-latest, armv7-unknown-linux-gnueabihf)	9m 40s
cargo test (ubuntu-latest, armv5te-unknown-linux-gnueabi)	11m 34s
cargo test (ubuntu-latest, i686-unknown-linux-gnu)	4m 58s
	1h 31m 8s

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