top: add another tiny bit of robustness to rcfile code

top: add another tiny bit of robustness to rcfile code

At this point I don't know if the Rc.id ever carried a
value of 'b', 'c', 'd' or 'e' in a public release. But
I do know that those values ought not to be recognized
in any configuration file. Now they won't be for sure.

[ while the absence of this new check didn't produce ]
[ an error message, it would skip the initialization ]
[ of default values plus possible string extensions. ]

Signed-off-by: Jim Warner <james.warner@comcast.net>