prevent seg faults when running with Electric Fence.

The "more" brigade (created by apr_brigade_split after seeing a FLUSH bucket)
was in the deferred_write_pool.  d_w_p is cleared, "more" is copied into b,
then the while loop test for APR_BRIGADE_EMPTY(b) blows up.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@97484 13f79535-47bb-0310-9956-ffa450edef68