Fix get_prefix empty reply

Fix get_prefix empty reply

Author: chillymosh

docs/changelog.rst

@@ -1,5 +1,12 @@
 :orphan:
 
+Master
+======
+- TwitchIO
+    - Bug fixes
+        - Fix IndexError when getting prefix when empty message is sent in a reply.
+
+
 2.7.0
 ======
 - TwitchIO

twitchio/ext/commands/bot.py

@@ -173,7 +173,9 @@ async def get_prefix(self, message):
         prefixes = await self.__get_prefixes__(message)
         message_content = message.content
         if "reply-parent-msg-id" in message.tags:
-            message_content = message_content.split(" ", 1)[1]
+            message_content = " ".join(message.content.split(" ")[1:])
+        else:
+            message_content = message.content
         if not isinstance(prefixes, str):
             for prefix in prefixes:
                 if message_content.startswith(prefix):