MINOR: startup: don't rely on PR_STNEW to check for listeners

MINOR: startup: don't rely on PR_STNEW to check for listeners

Instead of looking at listeners in proxies in PR_STNEW state, we'd
rather check for listeners in those not in PR_STSTOPPED as it's only
this state which indicates the proxy was disabled. And let's check
the listeners count instead of testing the list's head.