Bug 20875: (bug 16735 follow-up) Fix library list for OpacAddMastheadLibraryPulldown

Bug 20875: (bug 16735 follow-up) Fix library list for OpacAddMastheadLibraryPulldown

This patch fixes a regression introduced by
  commit 2059f7d8016ab61172830e9b670279d3e28882b7
  Bug 16735: Migrate library search groups into the new hierarchical groups

It re-added code that was removed by bug 15758 (use of var BranchesLoop).

Test plan:
- Create library search groups
- Turn OpacAddMastheadLibraryPulldown on
- At the OPAC confirm that the search box with libraries and library
groups is displayed and works correctly.
- Remove the library search group
- The dropdown list should not have the optgroup tags

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>