Fix re-verifying signature after importing key in verification result dialog

When the key lookup dialog closes, the QProgressDialog that shows the lookup progress receives as Close event,
which makes it emit canceled, which triggers our cancel logic - ultimately resulting in the new certificate being
processed directly. The patch breaks this chain by returning early if the progress is -1,
which it only is if the dialog was reset after finishing

• GnuPG-Bug-ID: T7429