Bug 21064: Use undefined instead of undef

Bug 21064: Use undefined instead of undef

To test:
1 - Load the advanced cataloging editor
2 - Refresh the page several times
3 - Check the JS console, you shoudl see an error:
    'undef is not defined'
4 - Apply patch
5 - Try again, should be no error

Signed-off-by: Pierre-Luc Lapointe <pierreluc.lapointe@inLibro.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
(cherry picked from commit 367f47c416fa9164ccb8d9e5f50772e5a516d6b7)
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
(cherry picked from commit f60c611972fe0442ee66f6ebf3a40f00bd11efcc)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>