Fix unbalanced new/free() -> new/delete

(Spotted while valgrinding an unrelated issue)

Change-Id: I2eab4c08e251d79f427fd01442c4dce20d7d89f0
Reviewed-on: https://gerrit.libreoffice.org/11785
Reviewed-by: David Tardon <dtardon@redhat.com>
Tested-by: David Tardon <dtardon@redhat.com>