Add another test case to TestRSA and make it pass

Looks like jsbn doesn't work well with typed arrays. The fix here is straightforward but probably not very good performance-wise, to optimize it we would probably need to modify jsbn (it is not a well documented nor well readable library, so I'd do that only if it will be really necessary).
Yes, jsbn may produce a string with an odd number of characters (0 as a leading character is ignored by jsbn).