Bug in lznt1.py causes infinite loop

[crankyflamingo]

Came across an xshell sample that caused the LZNT1 compression to infinitely loop.
In the below code, len(tmp) was 0.
(line 85 ish)

if length >= bp:
    tmp = u[-bp:]
    while length >= len(tmp):
        u += tmp
        length -= len(tmp)
        if not len(tmp):  <- added in fixes the issue.
            break

    u += tmp[:length]

Thanks.