Catch all ZOOM::event() return values less than 1. This includes -4

Catch all ZOOM::event() return values less than 1.  This includes -4
	(too many connections), which was the cause of the busy-loop
	failure when testing all targets.
Final play-out of left-over events also avoids busy looping on
	unexpected negative return-value.
Do not re-enter main loop after initial exit.