Fix crash when last yielded value is a closure

Fix crash when last yielded value is a closure

If zend_generator_close is called from within zend_generator_resume (e.g.
due to a return statement) then all the EGs will still be using the values
from the generator. That's why the stack frame has to be the last thing
that is dtored, otherwise some other dtor that is using
EG(current_execute_data) might access the already freed memory segment.
This was the case with the closure dtor.

The fix is to move the dtors for key and value to the start of the handler.
This way the stack frame is the last thing that is freed.