LP#1845050: fix issue where reports interface was partially loaded

LP#1845050: fix issue where reports interface was partially loaded

This patch adjusts mod_xmlent to not free its XML parser
prematurely in the face of an EOS bucket received while processing
a sub-request.

To test
-------
[1] Test on a platform that has Apache 2.4.25 or later, such as
    Debian Stretch.
[2] Note that when loading the reports interface that the source
    of the frame containing oils_rpt.xhtml is incomplete and that
    actions like creating a template or folder do not work in the
    interface.
[3] Apply the patch and repeat step 2. This time, oils_rpt.xhtml
    should be fully loaded and the interface fuctional.

Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>