logger: use newer, more robust IRC connection check

The revamped `connection_registered` bot property checks for a backend,
a socket connection, AND connection registration. This is what we need
to prevent doing a `say()` before the IRC connection is ready.

sopel/logger.py

@@ -29,8 +29,8 @@ def emit(self, record):
         :param record: the log record to output
         :type record: :class:`logging.LogRecord`
         """
-        if self._bot.backend is None or not self._bot.backend.is_connected():
-            # Don't emit logs when the bot is not connected.
+        if not self._bot.connection_registered:
+            # Don't emit logs to IRC when the bot is not connected & registered.
             return
 
         try: