wks: Make sure that ERR is always initialized.

* tools/wks-util.c (install_key_from_spec_file): Initialize ERR in case
the loop is never run.

This is part of

(cherry picked from commit 021c27510b52f86a95ae70b5f4ed5d2c3886c3e8)

• GnuPG-bug-id: T7129
• Co-authored-by: Jakub Jelen <jjelen@redhat.com>