ircbot.rb: fix reconnect logic

ircbot.rb: fix reconnect logic

connect calls stop_server_pings, which resets @last_rec, and if
@socket.connect raises exception, @last_rec remains nil, and reconnect
will not wait for next try, causing hundreds of reconnect tries per
second, which the logger thread cannot process fast enough, leading
to memory leaks (growing $log_queue).