Do not crash on privmsg with no content

There is a corner case (/dcc chat) where a privmsg can have no content.
Ignore such corner cases instead of crashing.

Change-Id: Ia07c76c4a2342bb4e7bc9c37a4944d4b9f18efd8

ptgbot/bot.py

@@ -96,6 +96,9 @@ class PTGBot(SASL, SSL, irc.bot.SingleServerIRCBot):
         nick = e.source.split('!')[0]
         msg = e.arguments[0][1:]
         words = msg.split()
+        if len(words) < 1:
+            self.log.debug("Ignoring privmsg with no content")
+            return
         cmd = words[0].lower()
         words.pop(0)