(CFACT-145) Fix segfault when libruby is not found.

When setting up whether or not stack traces should be printed with
exception messages, we set the option on the ruby object outside of
where it is being checked for null.

The fix is simply to move the line up inside the block where ruby is
valid.
Merge pull request #230 from peterhuene/cfact/145

(CFACT-145) Fix segfault when libruby is not found.