Update context.py

Author: plun1331

discord/commands/context.py

@@ -109,6 +109,9 @@ def author(self) -> Optional[Union[Member, User]]:
 
     @property
     def voice_client(self):
+        if self.guild is None:
+            return None
+        
         return self.guild.voice_client
 
     @cached_property