Whenever ->last_unsafe is set to `true` an exception has been thrown. Thus we
can replace the check for `->last_unsafe` with a check for `EG(exception)`
which is a much more natural way to ommunicate an error up the chain.
When Radomizer::__construct() was called with no arguments, Randomizer\Engine\Secure was implicitly instantiate and memory was leaking.
Co-authored-by: Tim Düsterhus <timwolla@googlemail.com>
Tim Düsterhus