Fix bad proxy expiration calculation. HTCONDOR-519
Fix bad proxy expiration calculation. HTCONDOR-519

The non-macOS code path had the wrong variable name.
Also fix a compiler warning.

htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor