lastchange: don't use git rev-parse output when it fails
lastchange: don't use git rev-parse output when it fails

If you weren't using SVN or Git, but you had Git installed,
we still thought you were using Git and had empty info for
the version number.

Review URL: http://codereview.chromium.org/6308016

git-svn-id: http://src.chromium.org/svn/trunk/src@72706 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: a514d803e485c5e422676072971583406755008f
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser