Bug 21476: Fix HTML5 media from playing in the OPAC - incorrect filters

Bug 21476: Fix HTML5 media from playing in the OPAC - incorrect filters

This patch makes a correction to a template filter to prevent
incorrectly-encoded HTML in media source links which were preventing
media from embedding correctly in the OPAC.

To test, apply the patch and enable the HTML5MediaEnabled and
HTML5MediaYouTube system preferences.

- Edit a record to include links to videos in 856$u. For example:
  - https://www.youtube.com/watch?v=grTwH6Evdfc
    - https://archive.org/download/POPEYEMeetsSindbadTheSailor1936/POPEYE%20meets%20Sindbad%20The%20Sailor%20%281936%29.ogv

    View the record in the OPAC and confirm that the videos display in
    the
    "Play media" tab and that they play correctly.

Tested and works as described, also matches the intranet code.

Signed-off-by: Alex Buckley <alexbuckley@catalyst.net.nz>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>