config.types: document empty except AttributeError clause

Fixes CodeQL py/empty-except alert.

Author: dgw

sopel/config/types.py

@@ -101,8 +101,10 @@ def configure_setting(self, name, prompt, default=NO_DEFAULT):
         attribute = getattr(self.__class__, name)
         if default is NO_DEFAULT and not attribute.is_secret:
             try:
+                # get current value of this setting to use as prompt default
                 default = getattr(self, name)
             except AttributeError:
+                # there is no current value; that's OK
                 pass
             except ValueError:
                 print('The configured value for this option was invalid.')