[Bugs report] Vec::pop is not exception safe

[iosmanthus]

The Vec::pop maybe fail while copying the object.

0xffff-lib/src/collections/vector.h

Lines 73 to 80 in 68c3123

	template <typename T>
	std::optional<T> Vec<T>::pop()
	{
	if (this->len > 0)
	return this->buf[this->len-- - 1];
	return {};
	}