The culprit is the too restrictive fix for bug #71536, which prevents
`php_libxml_streams_IO_write()` from properly executing when unclean
shutdown is flagged. A *more* suitable solution is to move the
`xmlwriter_free_resource_ptr()` call from the `free_obj` handler to an
added `dtor_obj` handler, to avoid to write to a closed stream in case
of late object freeing. This makes the `EG(active)` guard superfluous.
We also fix bug79029.phpt which has to use different variables for the
three parts to actually check the original shutdown issue.
Thanks to bwoebi and daverandom for helping to investigate this issue.
