Have server avoid sending empty data

While the client can handle it now, have the server
avoid needless processing of '' data from a console
provider.  Address it at the deepest level (the
tlvdata implementation) and a place higher up the stack
to avoid hits to log and such.

confluent_client/confluent/tlvdata.py

@@ -38,6 +38,9 @@ def send(handle, data):
     if isinstance(data, str):
         # plain text, e.g. console data
         tl = len(data)
+        if tl == 0:
+            # if you don't have anything to say, don't say anything at all
+            return
         if tl < 16777216:
             # type for string is '0', so we don't need
             # to xor anything in

confluent_server/confluent/consoleserver.py

@@ -347,6 +347,9 @@ class _ConsoleHandler(object):
             if data == conapi.ConsoleEvent.Disconnect:
                 self._got_disconnected()
             return
+        elif data == '':
+            # ignore empty strings from a cconsole provider
+            return
         if '\x1b[?1l' in data:  # request for ansi mode cursor keys
             self.appmodedetected = False
         if '\x1b[?1h' in data:  # remember the session wants the client to use