Don't return 0 as "time until next ping" when we've already sent a ping. return

None instead.

IRCBot.py

@@ -95,7 +95,9 @@ class Bot(object):
     def next_ping(self):
         timeouts = []
         for server in self.servers.values():
-            timeouts.append(server.until_next_ping())
+            timeout = server.until_next_ping()
+            if not timeout == None:
+                timeouts.append(timeout)
         if not timeouts:
             return None
         return min(timeouts)

IRCServer.py

@@ -228,6 +228,8 @@ class Server(object):
         return decoded_lines
 
     def until_next_ping(self):
+        if self.ping_sent:
+            return None
         return max(0, (self.last_read+PING_INTERVAL_SECONDS
             )-time.monotonic())
     def ping_due(self):