BUG: do not assume 0 is in index of potential Series
closes #7857... this time it checks also for a Series (and it passes all tests).

fyi, you don't normally need to close and reopen the PR, just force push, see here: https://github.com/pydata/pandas/wiki/Using-Git
 Thanks; OK for the force push in the future (just feared it was unpolite), but the page you linked doesn't mention it!
 no unless you are working with someone else then almost always better to force push (and if you are then someone needs to periodically rebase), just much cleaner that way IMHO.
