Mass mailing with zero recipients

Log hrs at http://dev.nysenate.gov/issues/6373.

If the mailing has 0 recipients, put up a 'formRule' error (text below) when user clicks "Next" to advance from Step 4 (Test) to Step 5 (Schedule or Send).
(Make sure we don't put up the error when they click Send Test Mailing OR Save and Continue Later.)

"You can not schedule or send this mailing because there are currently no recipients selected. Click 'Previous' to return to the Select Recipients step, OR click 'Save & Continue Later'."

— Original Post —
If a mass email has 0 recipients, the job starts but never completes; the status stays at "running."

But the real problem is that mailings with 0 recipients are allowed to start at all; they should be stopped at Step 2.