util.ringbuffer: find(): Fix find logic bugs If the buffer was full, find() would return earlier (wpos == rpos). Checking blen is the better way to test if the buffer is empty. Secondly, the loop scanned for blen - l, but if l (length of needle) was larger than the buffer length, this calculation would underflow and cause a lot of spinning. New tests have been added to cover various edge cases of :find().