Fix a trailing slash/last filename truncation bug observed on Linux,

  Fix a trailing slash/last filename truncation bug observed on Linux,
  which affected DAV MOVE operations and even general file access.
  PR 14147, 10687, 10236 [Dan Good <debug@gooddan.com>]

  I'm accepting Jeff Trawick's suggestion of twisting the test into an
  assert, since it seems very unlikely (after correctly resetting the flag)
  that this will fault.

Reviewed by:  Jeff Trawick, Will Rowe

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@97366 13f79535-47bb-0310-9956-ffa450edef68