Bug 21036: Fix uninitialized value within @itemnumber in string ne

Bug 21036: Fix uninitialized value within @itemnumber in string ne

Line from 16.11 log:
Use of uninitialized value within @itemnumber in string ne at /usr/share/koha/prodclone/reserve/modrequest.pl line 70.

Test plan:
Read the change. Not 100% identical (numeric zero) but should be enough.
This line is probably not needed at all.

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
(cherry picked from commit 4560d9623663e9fd0b60f9a39ec53082cdd90f24)
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>