Fix message parameters edge case

Sometimes an incoming message won't have any content (for some reason).
I haven't looked too deeply into the origins of it. This just bypasses
that case and returns early.

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

omnibot/bot.py

@@ -193,6 +193,8 @@ class Bot:
         if who.nick == self.server_config.nick:
             # Don't raise on_message events for ourselves
             return
+        if len(message.paremeters) == 1:
+            return
         line = message.parameters[1]
 
         # TL;DR OF THE BELOW: if the first parameter looks like a channel in