Bug 16651: Notes field blank for 952$z in opac-course-details.pl

Bug 16651: Notes field blank for 952$z in opac-course-details.pl

This patch changes course reserves to check for item notes form the
course reserve and fallback to itemlevel notes if they are empty

To test:
1 - Enabvle course reserves
2 - Add some items
3 - Make sure the items have notes at the item level and not at course
reserves
4 - Notes don't display in staff or opac
5 - Apply patch
6 - Notes display in staff and opac
7 - Add notes at course reserves level
8 - These override the item level notes

Signed-off-by: Hector Castro <hector.hecaxmmx@gmail.com>
Works as advertised

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
(cherry picked from commit 62508428cdf3a4c3da975ef5f88c8ece9cf50537)
Signed-off-by: Frédéric Demians <f.demians@tamil.fr>