Bug 5376: Batch Mod and Delete require superlibrarian permissions

Bug 5376: Batch Mod and Delete require superlibrarian permissions

This only occurs with IndependantBranches turned on; in an attempt to check that the items being
modified belonged to the user's branch, the code made a simultaneous comparison and assignment,
which is not permitted in all compilations of Perl.

Splitting the assignment of $itembranchcode and the check for its non-null value fixes the problem

Signed-off-by: Nicole Engard <nengard@bywatersolutions.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>