Squelch uninitialized var warning from hold_copy_targeter

Squelch uninitialized var warning from hold_copy_targeter

open-ils.storage_stderr.log was getting filled with entries like:

"Use of uninitialized value in concatenation (.) or string at
/usr/local/share/perl/5.10.1/OpenILS/Application/Storage/Publisher/action.pm"

... consuming disk space endlessly. Stop that!

(Stealing Lebbeous' footwork and providing a slightly different solution.)

Signed-off-by: Bill Erickson <berick@esilibrary.com>
Signed-off-by: Ben Shum <bshum@biblio.org>
Signed-off-by: Dan Scott <dscott@laurentian.ca>