AFAICT, we have never created server configs of _all_ modules for _all_
  contexts, only when they come up (e.g., a directive of that particular
  module is provided) with the except that vhost containers complete the
  initialization of all modules.  I haven't stepped this, but it appears
  to be correct.

  This patch assures we can merge two incomplete directory sections
  together.  They will (obviously) need to be merged with a LHS default,
  e.g. a vhost's or main server's default dir config.  That's fine, this
  just allows either the LHS or RHS value to be null, and for merging to
  still succeed.

Reported by:  Sander Striker <striker@apache.org>
Additional Analysis:  Doug MacEachern


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@91098 13f79535-47bb-0310-9956-ffa450edef68