util: skip base after base-test

If, for whatever reason, our base-detection supports more than 36, we
should just continue. There is no reason to fail. We only do that to
protect against wrong user-input.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
util: return U*_MAX on atoi overflow

If an atoi() helper detects an overflow, don't return garbage but return
the maximum value instead. Otherwise, our returned values are
non-deterministic (well, almost..) and no-one can make use of them. With
U*_MAX at least some users will be happy.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>