make take_while function unsafe

[kitcatier]

Hello, I found a soundness issue in this crate.

email-parser/email-parser/src/parsing/combinators.rs

Lines 85 to 100 in 0e72550

	pub fn take_while<F>(input: &[u8], mut condition: F) -> Res<&str>
	where
	F: FnMut(u8) -> bool,
	{
	for i in 0..input.len() {
	unsafe {
	if !condition(*input.get_unchecked(i)) {
	return Ok((
	input.get_unchecked(i..),
	std::str::from_utf8_unchecked(input.get_unchecked(..i)),
	));
	}
	}
	}
	Ok((&[], unsafe { std::str::from_utf8_unchecked(input) }))
	}

The unsafe function called needs to ensure that the parameter must be:

• The bytes passed in must be valid UTF-8.
  https://doc.rust-lang.org/std/str/fn.from_utf8_unchecked.html
  When the parameter condition panics, the input will be saved as non-utf8, which may cause undefined behavior in multi-threaded programs. The developer who calls the take_while function may not notice this safety requirement.
  Marking them unsafe also means that callers must make sure they know what they're doing.

[Mubelotix]

Hi, thank you for your input. It is known there are several soundness issues like that one in this crate. I'm also suspecting some safety issues. This is due to me being a beginner when I started it and wanting to prioritize performance over everything else. I have been working on a v2 on another branch that will fix everything.

[Mubelotix]

Closing in favor of #13