[commands] GroupView.get_command shouldn't raise errors for empty names

discord/ext/commands/core.py

@@ -1180,6 +1180,8 @@ class GroupMixin:
             return self.all_commands.get(name)
 
         names = name.split()
+        if not names:
+            return None
         obj = self.all_commands.get(names[0])
         if not isinstance(obj, GroupMixin):
             return obj