Only write the nick change event on channels that actually have the nick on the channel

This should prevent nick changes appearing in logs that don't have the
user on the channel.

logbot.py

@@ -199,7 +199,10 @@ class Logbot(SingleServerIRCBot):
 
     def write_event(self, name, event, params={}):
         # Format the event properly
-        chans = event.target()
+        if name == 'nick':
+          chans = params["%chan%"]
+        else:
+          chans = event.target()
         msg = self.format_event(name, event, params)
         msg = urlify2(msg)
 
@@ -323,10 +326,15 @@ class Logbot(SingleServerIRCBot):
                          })
 
     def on_nick(self, c, e):
-        self.write_event("nick", e,
-                         {"%old%" : nm_to_n(e.source()),
-                          "%new%" : e.target(),
-                         })
+        old_nick = nm_to_n(e.source())
+        # Only write the event on channels that actually had the user in the channel
+        for chan in self.channels:
+            if old_nick in [x.lstrip('~%&@+') for x in self.channels[chan].users()]:
+                self.write_event("nick", e,
+                             {"%old%" : old_nick,
+                              "%new%" : e.target(),
+                              "%chan%": chan,
+                             })
 
     def on_part(self, c, e):
         self.write_event("part", e)