Extracting a PyReadWriteArray can panic for no reason

[flying-sheep]

This should just use .try_readwrite()? instead:

rust-numpy/src/borrow/mod.rs

Lines 483 to 492 in 4ef0102

	impl<'a, 'py, T: Element + 'a, D: Dimension + 'a> FromPyObject<'a, 'py>
	for PyReadwriteArray<'py, T, D>
	{
	type Error = CastError<'a, 'py>;
	fn extract(obj: Borrowed<'a, 'py, PyAny>) -> Result<Self, Self::Error> {
	let array = obj.cast::<PyArray<T, D>>()?;
	Ok(array.readwrite())
	}
	}

Related: #527