Try to overpay the recipient if we fail to find a path at all

Try to overpay the recipient if we fail to find a path at all

Previously we'd only try to overpay if we managed to find a path
to the recipient which was sufficient. However, if we fail to find
any path to the recipient at all we should still retry overpaying
the recipient. Ultimately we should be silling to pay whatever
reasonable performance penalty if the alternative is not finding a
path at all, which we do here.