phrevset: fix code that was returning commit strings
Fix another code path in phrevset that could incorrectly return commit strings
instead of rev numbers.
Manually tweaked phrevset to force it to hit this code path (to ensure it would
not find the commit from the local log walk first), and confirmed it now
returned a rev ID instead of commit strings.
Reviewers: #fbhgext, quark, durham
Reviewed By: #fbhgext, quark
Differential Revision: https://phab.mercurial-scm.org/D684