Don't attempt to encode topic to utf-8 twice.

Thanks to Luc Milland.

Change-Id: I954db79a6cf332350337c5147ac716cb3e6c4e2a

ChangeLog.txt

@@ -4,6 +4,7 @@ v1.0.2
 - Fix "protocol" not being used in publish.single()
 - Fix Client constructor for the case where "localhost" is unresolvable.
   Closes #439277.
+- Don't attempt to encode topic to utf-8 twice.
 
 v1.0.1
 ======

src/paho/mqtt/client.py

@@ -1656,7 +1656,7 @@ class Client(object):
             remaining_length = remaining_length + 2
 
         self._pack_remaining_length(packet, remaining_length)
-        self._pack_str16(packet, utopic)
+        self._pack_str16(packet, topic)
 
         if qos > 0:
             # For message id